whats the best way to go about gathering cards other then buying them?

arena

Starting out i did a lot of the hidden quests like hitting lvl 10 and then lvl 10 on all completing all vs normal and all vs expert

then do daily quests atleast every 2 days make sure u reroll 40-50 for 60 or the spectate etc.

Only if you actually know what youre doing

dont waste your money in arena
first you need to play in ranked for a bit, do the hidden quests (google)
then, when you think you're doing good, play your free arena
then, if you like it, play more arenas

Arena is by far your best way of building a collection. But it's not easy to jump into Arena as a new player and be successful. I suggest watching streams on Twitch that are Arena focused and learn from better players. Then after you get a good grasp on the format, try it out and see how well you do. There are a lot of Arena resources out there to help build a good deck.