Okay, to make understanding Skyler and his world a little better, I'm going to list anything important you might like to know here. That being terminology and characters and such.
Terms of the World
Croagunk's Swap Shop: Shop run by Croagunk in the guild. Trade for various ability enhancing items in the Swap Cauldron.
Crystal Cave: As the name suggests, a cave that has many crystals. Also the location of a hidden lake guarded by Azelf, because a Time Gear is found there.
Dusk Forest: A forest in the dark future. Apparently home to Celebi. Passing through the forest will lead you to a Passage of Time.
Fogbound Lake: A lake who's existence has only recently become common knowledge. It's guarded by Uxie because it's home to a Time Gear.
Hidden Land: A mysterious land hidden in the space between seconds(don't ask me how that works) and home to Temporal Tower. Only those who meet the requirements are able to go there.
Hot Spring: Place visited by all sorts of weary Pokemon. Torkoal can usually be found warming himself on the rocks there.
Mystery Dungeon: A place in the world that Pokemon live in or explore, that changes layout with every visit. All missions and explorations take place here.
Quicksand Desert: Located beyond the Northern Desert. Home to an underground lake guarded by Mesprit where a Time Gear rests.
Recycle Shop: Run by Wynaut and Wobbuffet. Explorers recycle several items they don't need for other items or Prize Tickets.
Sharpedo Bluff The partner Pokemon's old house. From the sea the bluff looks exactly like the Pokemon Sharpedo.
Spinda's Juice Bar: A place to enjoy a refreshing drink. Bring any food item and Spinda will turn it into an enjoyable or even amazing drink.
Temporal Tower: Home to Dialga and the physical manifestation of time. It the tower were to collapse then time would stop all over the planet.
Treasure Town: More of a town market than a town. Where all exploration teams do most of their preparation for exploring. Features a bank, dojo, storage, daycare, two shops, move linking shop, and a treasure box appraisal.
Wigglytuff's Guild: The place near Treasure Town where requests for help and outlaw wanted posters are posted. The guild also provides training for would-be explorers. Visitors have their footprints evaluated before being allowed into the building.
Notable Items and Such
Berries: Restoratives. They restore health or cure various ailments when eaten.
Dimensional Hole: Portal that enables time travel. Presumably opens straight from starting point to destination. Attacking one can have unpredictable effects.
Dimensional Scream: Rare ability. A being with this ability may experience a dizzy spell and then see and/or hear an event in the past or future, triggered by touching a person or thing that the event relates to. The ability does not work on-demand, and it's effect changed between the dark future and the past. The ability does not work at all unless the user is in the presence of a person that they trust.
Explorer Badge: Mark of an explorer. Has magical powers to help in rescue missions.
Footprint Runes: Messages inscribed using the footprints of various Pokemon.
Gummi: Favorite snack food of Pokemon that also makes them smarter. Each type of Pokemon has at least two favorite kinds.
Orbs: Magical spheres that have various useful abilities.
Passage of Time: Cliche huh? This passage leads from the future to the past. It's unknown if there are any in the past or if it's only in the dark future. Launching attacks into them can have unpredictable results.
Perfect Apples: Very large and delicious apples. But more than that, they're the Guildmaster's favorite food. If there were no Perfect Apples, then Guildmaster would.............Yes, that's what would happen.
Rainbow Stoneship: A large circular slab of stone that carries the rider to the foot of Temporal Tower from the Ancient Ruins in the Hidden Land. Predictably, it leaves a rainbow in its wake as it flies.
Relic Fragment: Personal treasure of Skyler's partner. A small piece of stone with a distinct pattern. It serves as both proof to enter the Hidden Land, and the key to activating the Rainbow Stoneship.
Seeds: ...seeds. They have effects though and are very useful to help you or hurt others...if you can tell them apart.
Swap Cauldron: Found in Croagunk's Swap Shop. Drop the items you want to swap in it and a different item pops out...again, don't ask me how.
Time Gears: Strange glowing gears. Found hidden in certain regions, they help keep time flowing naturally. Taking one from its altar results in time stooping in its designated area.
Treasure Bag: Magic bag used by explorers...can you say bag of holding? That's what it is~
Unown Language: Symbols taken from the various shapes of the Pokemon, Unown.
Wonder Map: A map that shows the layout of the land. Unknown areas are shown under cloud cover which moves once the area is explored. It's a wonder of a convenience!
Meet the People
Azelf: Guardian of the Crystal Cave Time Gear. She's pretty smart, but Grovyle nearly killed her because of it.
Azurill: Youngest of two brothers. He's very nice, but trouble seems to find him and his brother very easily. He looks up to Skyler and his partner because they keep coming to help.
Bidoof: Yup yup! By golly! Bidoof was the newest apprentice before Skyler and his partner. He enjoys helping they where he can and is a big eater and a bit emotional.
Celebi: A shiny Celebi from the dark future. She seems pretty carefree and has a crush on our favorite Time Gear thief. Unfortunately, he seems oblivious.
Chatot: Head of intelligence and Wigglytuff's right-hand Pokemon. He gives all the directions, but says a lot under his breath when he thinks oddly of others. He's a little uptight, but looks out for all guildmembers.
Chimecho: Yay! She's an apprentice in charge of making dinner and run the team assembly at the guild. She's quiet and cheerful, and seems to be very fond of the guildmaster.
Corphish: Hey hey! Corphish is another apprentice. He's a hard worker and likes to jump right into new things.
Croagunk: The loner apprentice who runs the Swap Shop. He tends to chuckle eerily, but is a pretty nice guy.
Dialga: Pokemon ruling over time. He lives atop Temporal Tower. Even though he rules time, the effect of time stopping has disastrous effects on his being.
Diglett: Apprentice and guild sentry. He can identify nearly every Pokemon by footprint...but he doesn't know what he doesn't know.
Drowzee: The first outlaw Skyler's team ever arrested. He's a good actor apparently.
Dugtrio: Apprentice, Diglett's dad, and the one who updates the notice boards. They are very proud of their son and take great pride in their duty.
Dusknoir: An agent sent by Primal Dialga to capture Grovyle and Skyler. He liedto everyone to do so and nearly put an end to Grovyle, Skyler, and Skyler's partner. He's cunning, but is he truly evil?
Grovyle the Thief: Formerly Skyler's partner. He was gathering the Time Gears to prevent the planet's paralysis. His impatience is makes him not stop to explain and he seems to be missing something right under his nose.
Guildmaster Wigglytuff: Friendly friends~ Wigglytuff is the guildmaster and a renowned explorer. His demeanor makes him really hard to read. He's friendly and a little odd, but he's also very powerful and has a BIG temper.
Loudred: Obnoxiously loud! Loudred is an apprentice who serves as the guild's gatekeeper. He's loud and kind of gruff, but isn't a bad guy. He does wakes in the morning though so don't expect to sleep in.
Marill: Oldest of two brothers. He's very nice, but trouble seems to find him and his brother very easily. He looks up to Skyler and his partner because they keep coming to help.
Mesprit: Guardian of the Quicksand Desert Time Gear. She's nice, but takes her job very seriously. She can jump to conclusions quickly, which may lead to trouble...
Primal Dialga: Dialga after he's lost his reason in the dark future. His only concern is his own survival, so he'll do whatever it takes to keep history from being changed.
Spinda: Primary owner of Spinda's Cafe. Not sure on the gender, but this Pokemon is hyped on hopes and dreams related to explorers and seeks to make it more fun and profitable for everyone to explore. Can also make any number of awesome drinks if you supply the ingredient.
Sunflora: Oh my gosh! Sunflora is the most experienced of the guild's apprentices and good for advice. Her nature is really outgoing, making her usually easy to get along with.
Team Skull: A team of crooks and bullies.They hassled Skyler's team as much as possible, but displayed some redeeming qualities at the very end...
Uxie Guardian of the Fogbound Lake Time Gear. He has the power to wipe your memory clean apparently. Hmmm...
Wobbuffet: That's right! Alongside Wynaut, she runs the Recycle Shop in Spinda's Cafe. Her job is to determine who wins in Prize Tickets.
Wynaut: Why not [insert action here]? Wynaut is the main Pokemon in charge of the Recycle Shop. Se's cheerful and obviously likes this job, so why noy pay her a visit?