Right I hate this reddit downvote "OOh he had a problem with the game!!! HOW F**KING DARE HE COMPLAIN!!" so much (Seriously if you do this you will always be a number) so:
Hold E to pick an item up, and press R to put it in your inventory. While holding an item, you can press Mouse1 to throw it (or use while in the main hand) and hold Mouse2 to rotate it. Scroll wheel is reserved for going through the inventory at the top or scrolling through the hover-menu when hovering over an item. E is the default button for pretty much everything, so if you're out of ideas try that one first. The control scheme is similar to how Garry's Mod handles, so you can look there as well to get a better grasp.
I'm not going to hold it against you because it can be rather clunky to get down when you start playing, I don't get why these discord addicted hobgoblins are. Probably lost touch with reality.
I hope you can still enjoy it in spite of the barrier control scheme, there's a lot to this game. Youtube can only give half the experience really.