The car belongs to a car sharing company. In Munich for example there is Share Now, Miles, Sixt Share, and some specialized ones. The cars are parked all over the city in normal parking spots on the side of the road. Using the app, you find the closest one, usually you'll find 2 or 3 within 500 meters (strongly depending where you are). You select it in the app, walk up to the car, use the app to unlock and are ready to go.
They are usually paid by the minute, but there is also packages for multiple hours or days. But I think for renting over multiply days, normal car renting is better. Sixt is pretty good. Takes no more than 5 minutes to pick up the car. You don't reserve a specific type, but a class of car. And when I reserve the cheapest class, until now I was upgraded to the higher class every single time. They even have a "Lucky Class" which will explicitly get you whatever they have available, up to the really nice ones.
Inside of the city, they can be parked in any public parking (mostly on street), and you can find them in the app. Just checked, to give a point of reference, and there are two cars available within 200 meters of my apartment, and 7 available within 500 meters. There are also special parking lots at the airport where car sharing cars park.
You can also have one delivered to you at a particular time, but that costs €30, and makes it where a taxi would be cheaper.
I also have to admit that probably 90% of my annoyances comes from a mental issue I have where it really, really bothers me when I think something could be more efficient than it is, when I'm not impacted.