The Pioneer format consists of all standard legal cards from Return to Ravnica, forward, except for fetchlands.

There is a small ban-list as well, which you can find here:

https://magic.wizards.com/en/banned-restricted-list

If none of that makes sense, don't worry! Just come join us for a game and we'll be happy to teach you.

To find the top decks in the Pioneer format, check out these links:
https://mtgdecks.net/Pioneer

https://www.mtggoldfish.com/metagame/pioneer#paper

To find even MORE resources, check out https://playingpioneer.com/ .