Acquiring good vehicles can make your experience with Saints Row much easier. This page of the guide explains how to steal cars, both parked and driven by NPCs. You'll also learn how to acquire free vehicles.
A separate page of our guide, Saving vehicles - how?, contains information on how to save stolen vehicles in your garage.
Stealing parked vehicles is a walk in the park - you don't need any lockpicks or tools to do so. All you need to do is approach the vehicle in question and press the interaction button.
Stealing moving vehicles requires a bit more effort, as you need to wait for it to stop or block its path somehow. Press the interaction button to throw out the driver.
Be careful - the driver may try to get their car back, so you should drive away from the scene ASAP. Someone might also end up calling the police, increasing your Notoriety. Stealing cars is inadvisable if you don't want to get in trouble with the law.
You'll obtain some free vehicles by simply progressing through the game. The first free car you'll acquire is the Ridgelord pick-up, obtained automatically and permanently by completing the prologue.
Finishing optional activities can also reward you with vehicles. For example, the Pony Express Side Hustles let you unlock different kinds of buggies.