In need of a ride, but don't feel like buying one or waiting for a taxi?
Parked NPC vehicles can be broken into by using a lockpick or advanced lockpick when next to them. A mini-game will pop up requiring you to successfully beat it before the doors will unlock. Once inside, you must hotwire the vehicle in a similar fashion by pressing "E".
To jack a car, you need to hold the driver up by pointing a firearm at them. They (and any passengers) will exit the vehicle and surrender. This will allow you to use your 3rd eye to target them and search them for keys. Once you have the keys, the vehicle will be unlocked & driveable.
Player vehicles parked in a parking lot are unable to be stolen. Lockpicks will not work on them, and they cannot be towed unless a LEO requests it.
Player vehicles parked outside of designated parking lots can be lockpicked and hotwired.
The Shady People give missions to steal High-Value cars. This job can only be done when there are at least two active police officers.