on steam trades, people ask for currency, steam items. but wtf is "Ref"

If you play it you get free weapon drops, you can make scrap out of it and with that ref.

You can also try to use gems. They are more easily controlled and you don't have to dig through half the internet to find out where to buy the damn thing (refs are not sold on the market, at least I sure as hell never found 'em). The problem with gems is that their price is more fluctuating (for example, 6 weeks ago 1000 gems were €0.80-0.83, now they are €0.69).

wait wtf is that!?

Hah yeah this one too. Actually just realized that I never even manged to figure this one out--and probably wouldn't have gotten it if not for your other post.