Hehe! You're doing fine! Just takes a little getting used to.
Here's where the red plastic and the footprint are:
Click and drag over the white line below to view the hidden spoiler text!
At the alley, look on the ground near the rear passenger door and you'll see a shadowy footprint. The first time you click on it, you can pick up the red plastic with the tweezers. After that, click on it again and collect the footprint itself. If you still cant see it, try backing farther away from the cab so you get a better view of the ground.
Good luck and enjoy!