It is very expensive to get the license in Japan (200,000 ~ 400,000 yen) if you go to a qualified driving school. Most Japanese do not know that you can get the license without going to any school. If you know how to drive in your own country, and just need the Japanese license, you can take exams at the drivers license center directly. If you can pass them once, you just pay for the exams and related paper works. I personally failed 10 times, but still just paid about 100,000 yen in total.
Most Japanese buy second-handed cars from dealers, who charges a lot for the paper work. If you do all the paper work by yourself, it is more than 10 times cheaper. My dealer did not allow me to do it by myself.
If your friends would like to sell his car to you, you can then do everything by yourself. If you have money but no time, hire a dealer and ask them to do the paper work. But why not just buy a new car then.
Things you need to do except for paying the money:
Old cars have to be inspected every two years by law. Otherwise, you can not drive it. Most Japanese do not know this can be done by themselves without a dealer. A dealer normally recommend you to change parts of your car as much as possible. The price ends up to be 3 or 4 times more expensive than what is really necessary. Check this web page in Japanese if you are interested to do it by yourself.
If the inspection of your car is already expired, get a temporary plate from the city hall so that you can drive it legally to the place for inspection.
Dealers pay very little for your car if you want to sell it. Sell it to another individual directly is a win-win situation for both of you.