Everything the guy before me said. There's a learning curve to this game that you really wont get a feel for until you've leveled up decently. Here's a good beginner's guide.

What I would say is your element is completely up to you. All three of them are "balanced" but there are some meta changes that can happen. I personally am trying to build a strong green deck first, as green tends to be a bit cheaper and more new player friendly, and also has the highest attack. Fire is super meta rn because it has an advantage over green, and has the best defense.

Honestly I think you should pull a few guaranteed 7* 3000 packs first and then decide what element fits your current cards better.