This page of the guide to Car Mechanic Simulator 2021 contains an instruction on how to store your cars in the game. You will learn how the Parking works.
Available: since the beginning of the game
Cost of additional alleys: 50000 CR
Parking is used to store the cars you own. You can't park customer cars for repair there. The first 10 slots are available immediately, but the next (alleys 1 and 2) have to be purchased.
To park your car, select the parking icon from the wheel menu.
Parking allows you to see the technicalities of your car...
...and also view it from the outside.