Press your use key to collect items. Default buton is "E". By the way, everybody can collect those items but if baiter/s collect 5 they get a "Fake Knife".

Yes but I can only pick up objects but it doesn't transform in a knife...

https://media.giphy.com/media/YSqzCrhSm8sREeqkLw/giphy.gif

So there is green collectible objects in the game. Not every map has them. But mostly maps starting with mu_ , md_ , murder_ have those green items. They randomly spawn around the world. Find them and get closer to them. And press "E" or USE key. When you collect it, the number on the bottom left increases by 1.

If you are a baiter, when that number gets to 5 you will realize that you have a Fake Knife in secondary weapon bar. Other than that green items are useless.

If you can't see green items type theese into your console:

mu_halo_loot 1
mu_halo_render 1

If you still have no green collectible objects in your map, that means the map you are playing doesn't support them.