You can buy in-game currency. People use Divine orbs as a trading currency; think of it as a dollar. There are other currencies, mostly less valuable then the Divine orb. Chaos orbs, annullment orbs, exalted orbs, think of those as a lesser currency.
A lot of the stuff you're going to get will not be super valuable, but you can also use a loot filter which will hide loot on the ground which doesn't have any significant value.
Do you plan on making your own build or following a guide? Which character class are you wanting to play? Do you like melee/ranged/magic type characters? Do you like to be tanky, or fast, etc.
90% of the unique items you find (similar to diablo in the sense there are unique items) won't have much value - but can be used in some instances depending on your build.
Suggestion would be to pick a class/type you want to play and find a guide to help you figure out what you need. Happy to provide more assistance. PM me and we could talk over discord if you like later.