You can also use the weekly free decks to rack up some IP. They're not groundbreaking, but they're definitely decent and playable. Spend the IP on collection packs, or, if you're looking for a specific card, find out which set has it and aim for that one.
But yeah, pretty much what Wayfinder said already. You can play bots if you fancy that sort of thing, or jump right into normal games.
Also, you can play with people you know or just challenge someone in chat. Or feel free to PM me (same IGN as here) and we can play a few games. I can give you some basic hints and pointers on deck building and gameplay.
Welcome to the game, hope you enjoy your stay.