If I buy a vehicle online, and I don’t have a garage, where does it go

Figured it out. Part of the problem was that the server situation on day one was preventing texts and calls from Simeon from triggering.

As you level he sends one telling you about purchasing a garage for your car. This happens at around levels 5-6. You can find all the properties by going to the in-game website: dynasty8realestate.com. The properties will also show up on the map if you drive close to them. They have a symbol that looks like a house; it's also very similar to the convince store icon.

By level 10 it looks like most of the available content has been opened up.

Heist are currently not available, and will arrive in a later update.

Installing a tracker allows you to see your car on the map. You can install a tracker at LS Customs, or you can get a free one when you store the car in your garage.

A tracked car can still be totaled or stolen. If this happens you are out of luck. Buying full coverage on your car at LS Customs gets around this. If the car is lost or stolen you can call up the insurance company and file a claim to get it back.

Each garage can hold a set amount of cars(between 2 and 10). Most cars you can steal can be stored in the garage. The game is a little restrictive on the high end cars-you have to buy them. I haven't tested it, but I assume you probably won't be able to store the bigger vehicles like semis and cargo trucks either. Physically they are probably too big to fit in the internal volume of the garages(at least the 2-car one I currently own)

Another bonus of the garage is you get a mechanic who can deliver a car from your garage to you anywhere on the map for $50.