New player that got back into the franchise. Any tips?

Check the limitless top meta decks to get an idea of what the current meta is about, and also ideas for your own decks.

This game doesn't support microtransactions so no you can't pay in-game to get cards.

To get cards directly from the game you can play the Ranked Ladder for rewards that include cards/packs and the Buy the Premium Battle Pass each tier gets you cards, packs and other in-game stuff.

You can also get packs (with cards) from code cards, when you get a code you can scan the code or type it in game, that will give you a pack that will get you cards.

If you have enough in-game currency you can craft specific cards too.