New to the game. Trouble understanding deck building

Delete if not allowed

I’ve only been playing a few weeks. I’ve spent probably 2500+ on cards and packs and everything else

The problem I’m having is building a deck. I have thousands of cards. But I have no idea what to look for, what goes into the decision making about adding a card to a deck.

I haven’t found much online. I’ve been playing different decks that I’ve tried to build against a friend of mine and have yet to win a single game

Any help is appreciated. Thanks