I was playing the trial, and this big dude surrounded by like 40 people was getting killed. I joined the group, killed him, and it said I received "Rift loot". I check in my bad, nothing is there. What is that?

Probably because you're playing on a trial account.

It's to try out the game, not get full access to it.

That's what I thought, but you never know

on the right side of your screen, theres a circle when you get "rift loot" and a button in the middle, click it and loot your phatz.