Does someone know an app or something which will allow me to store my cars without losing them
2 Answers
There is no certain way to get cars and not lose them. The only cars you will never lose are the Characters main vehicles which are usually spawned with them.
What you can do is buy a Garage, and store your cars in there when you're going to be exiting the game.
Or you can store them in the character's houses, as even the game tells you. The thing is you can only store one car at a non-bought garage.
Also note that if you destroy your car, or drive it in deep water, or park it outside a garage you will lose it(doesn't apply for the character's own cars (motorcycle) as explained in my first sentence).
2Using a garage will save your cars until you take the car out of your garage. If you need money for a garage then Just rob stores steal cars and sell them or complete missions.