Car novice

Hello Motor-Talk Forum, I’m new here and have a few questions that I could not answer about the search. So far we (woman, child and I) did not need a car because we lived within Cologne. If a car was needed we rented a rental car cheaply. Now we would like to, as we pull out, but buy a car know too little about it. For example, 200 000 km are “a lot” or not. The mileage per year would be at approx. 10000 km. How would a used car purchase take place. How does it work with registration car tax etc. With car rental this never played a role except for Europcar Sixt and Co. I am happy to hear from you and wish you a pleasant rest 🙂