Renting a car in Germany is easy if you have anything between 80€ to 150€ to burn. But its worth it with the amazing roads and beautiful scenery.
For longer trips
If you are a ADAC member it is a little cheaper to book a car from their website here:
If you are not a member of ADAC, then AVIS, EUROPCAR and SIXT are your options. Though from recommendations and experience ,SIXT is hassle free where as AVIS tends to be fussy while returning the car.
If you want a big (sedan) car you need to hold a driving license for more than 2 years. Else you will get something like a VW Polo, VW Golf, Mini, Ford focus, etc.
If you are a new driver it is recommended to get full insurance. Basically it will cover everything that you might do to the car. There are options with self payment e.g. till 850€ you have to pay or 0€ payment which exempts you from all expenses as a result of damage to the car. Needless to say, this will cost you more money; aprox 19€
You will get a car with a full tank which you will have to return with a full tank.
For short trips (Intracity)
They basically work on pay by minute basis. Normally you can buy prepaid minutes pack. Fuel and parking charges are included. You have have to register with these websites and they have a one time enrollment fee. These cars are parked throughout the city and can be accessed by access cards. They also have iOS and Android apps to locate the cars.
I use DriveNow and has a real good app. Best part is you get the latest BMW X1, 1 series or Mini to drive :D.
I have to try Car2Go, they have these small, cute but capable Smart cars
So happy driving folks!