They are found at various locations around the map. All traders and most gas stations have them as well as some bases.
Parking meter type: Park the vehicle on the small hologram at the parking meter.
Parking Bay type: Park the vehicle on the ramp.
The vehicle must have a key assigned to it.
Press F to access the parking menu. It will list the vehicles you have parked and will show the remaining lifespan of each.
Click the PARK tab while holding the key in your hand. You will see the name of the vehicle. It should be self explanatory from there.
Vehicles persist 45 days without interaction when they are in the garage. You can store up to 6 vehicles per player.
Vehicles left out of the garage only last 7 days regardless of being locked or being within range of a base flag.
** Vehicle parking meter kits are available ONLY to bases that are well established, active and able to be secured. Ask one of the admins if interested. Some rules apply.

Most importantly you must be able to secure it so that it can't be stolen. You can move it as often or as far as you wish, but the vehicle will NOT move with it. In other words, if you park a vehicle and then move the parking meter more than 100m from where you parked it, you will not be able to retrieve the vehicle. If you move it within 100M from where you parked it, lets say to adjust it to a nicer spot, it will work fine. If you want to move the parking meter more than 100M you MUST retrieve all parked vehicles first.