A cube is a curated collection of cards that is meant to be played together in a closed system, usually by building decks with the cards in the cube.
This particular cube is a 540 card non mutant (normal evolution rules apply), unlimited (Cards from the entire history of pokemon TCG allowed), non singleton pokémon cube.
A deck must contain exactly 60 cards. There are some other rules to keep in mind when building a deck:
Cube is usually played in 2 phases. In the first phase, players draft decks from the cards in the cube. In the second phase, players build decks from the cards they drafted and play against each other. There are a lot of different drafting systems your playgroup can choose and a lot of great resources on the internet that explain how they work. I recommend Lucky Paper's Cube draft format page where they list common draft formats and how many players they would work best with. Below are the ones I recommend and a short explainer on how they work.
Deal out N cards to each player, this is your "booster". Once each player has their "booster", each player takes one card from their "booster" and passes the rest to the left. Repeat as many times as you'd like, alternative which direction you're passing cards with each "booster". For Magic: The Gathering, booster drafts last for 3 rounds with each "booster" consisting of 15 cards.
Arrange cards into a 3x3 grid. Pick someone to go first. That individual picks a row or column from the grid. The remaining players pick from the remaining grid. Discard any remaining cards in the grid and repeat, rotating who picks first. Go as many rounds as you'd like (Recommendation, 18 rounds).
Deal N number of cards into N number of piles face up between all players. Pick someone to go first. That individual chooses one of the piles to add to their collection. Deal 1 face up card into each of the piles. The player to the left picks one of the piles and adds that to their collection. Repeat as many times as you'd like (Recommendation is to draft until each player has roughly 50-60 cards).
Part of the fun of cube is that you get to explore different card combinations and strategies each time. While this can be very rewarding it can also make playing a cube for the first time a bit daunting, esspecially if you're new to drafting or trading card games. Below are a couple of the combos and strategies that the cube was built to support. These suggestions aren't hard or fast rules, they're suggestions; Even if you don't end up with all of the cards listed in one of the sections below doesn't mean you can't try to make that combo or strategy work in your deck. Experimentation is the name of the game!

Thumping Snore is a powerful move capable of knocking out every pokemon in the cube. It's not without it's drawbacks as it puts Snorlax to sleep after being used. This is where Therapeutic Energy comes into play. In addition to recovering the status effects of the pokemon that it is attached to, it also prevents status effects from being applied on the pokemon. This means Thumping Snore won't put Snorlax to sleep!
Other cards you can pick to help faciliate this strategy might include Bouffalant, Hero's Cape, and Luxurious Cape among others.

United Wings cards all work off of each other, gaining strength the more of their allies are in your discard pile. While they start out weak, they'll grow in strength quickly and overwhelm your opponents with their low energy cost attacks that deal big damage. Cards like Phantump and Night Stretcher can help you recycle your United Wings attackers while Pokemon with the Refinement ability, like Kirlia and Gardevoir, or supporters like Professor's Research and Explorer's Guide can help you quickly put Pokemon with the United Wings attack into the discard pile.