If you find the "hidden" item, you can talk to Gaz (The rat in the truck), and this unlocks a SuperJump Mutation in his shop! Activate the jump via 'Q' in the side-Scrolling level. 

Cycle through dialogue with the "E" key (same as interacting with the environment).

The objective is to make it inside the Reactor!

(We didn't have time to introduce these things organically, and didn't want to cheapen the experience with tutorial pages).