Standard is the main competitive format for the Pokemon Trading Card Game. Only cards from the current legal sets can be used — a great starting point since you won't need every card ever printed! If you're new, don't worry: pre-built theme decks are a totally valid way to get started.
Video Game Championships uses the latest mainline Pokemon games. Battles are double battles — you bring 4 Pokemon and lead with 2. New to VGC? A great way to get started is practicing with friends using rental teams in casual play — just note that rental teams are not permitted in Championship Point-earning events like Cups and Challenges, so you'll want your own registered team for those.
GO events are played directly in the Pokemon GO app using GO Battle League rules. Bring your phone and get ready for some fast-paced battles! Championship Point-earning events like Cups and Challenges use Great League only. Ultra League and Master League are available for casual play during open league sessions.