After getting your 40'000$ money bag you want to go buy your neighbors car for around 23-24 grand.
You can do this by walking to them and hitting the f key.
The images I put was unrelated, just the smallest image I had.

You want to pull out of their drive way and drive to the gas station behind your house, its marked with a beacon like marker in your vision.
After that you should take it to the repair shop and fix it, the repair shop is almost if not adjacent to your home. Talk to the mechanic outside and he'll tell you the price of fixing it.
After that drive it to the green car outline and get out with f.
Then you go inside of your office and onto your computer, then you go under cars and renting, set it below the recommended rate to always have customers, 140 or 135 should do.

Once your car is ready for renting people will walk to it and if you talk to them you can rent it for the rate you put. Once they come back the gas will be drained and it will be damaged a bit. If you send it out on a full tank it should last 2 days. Fill up if it's not 70-60% full you should refill it.
If its damaged enough you can repair it and at that point you should just sell it after repairing.
But don't ask me about that. I only know how to rent.

I hope that this guide has helped if you didn't understand how the renting system worked.
But don't ask me about selling. I don't know how to do that yet. Might not ever. Maybe I will. probably not.