The Garage is where you can spawn the vehicles that you have purchased from the Car Dealership.
There are different types of garages available for vehicle spawning:
Do note that certain garages may have other vehicle types available, you can see the specific types by hovering over the garage in the pause menu map.
Special garage types may also appear as part of events.
M → Player Options → Interface Options → Toggle Legacy Garage. After that, the Sell Option should now appear in the Garage spawn menu.