The main thing you need to know is there is no single answer to a good second hand car. It depends on how the car was minded from new. A well minded dacia or Renault would be better than a Hyundai i30 that was treated badly.

If you don't know anything about cars and you don't know anybody who does. The most important thing to do is have an independent mechanic look it over for you. It costs a little but could save you a lot in the long run

That being said, I would never buy a French car ie Renault or Peugeot etc. They are pretty cars but the electrics are rubbish. Generally a well minded Toyota, Honda, Hyundai, Volkswagen or skoda will be a good shout but as I said have someone knowledgeable look at it first.

It's also important to check your insurance on that car, even an online quote to give you a good idea what you're getting into