Hi, thanks for using JustAnswer.com. Make sure you lube the belt with the poly lube that came with it or it will wear fast and be noisy. Now on to level..
There is a leg in each corner that will unscrew to raise the dishwasher. They can be hard to turn, so I would squirt a little WD-40 on the threads to ease in adjusting them. That should do the trick!
You didn't mention the plastic piece at all in your reply...
The feet basically align everything. The plastic piece is there to secure it to the cabinet so it wil not tip. You need to adjust the feet until it is propely positioned.