No worries. Most of the things you need to know about the way physics simulations work aren't actually taught until you take a course in numerical physics or modeling at the university level, so you aren't alone!
Here are the basics:
Friction: This sounds like it should be what you are looking for, but it is not. In computer games, "friction" is a retarding force between 2 physics objects, but since this is a top-down game, the "ground" is actually not a physics object. Therefore friction will not have any effect in a top-down 2D game.
Linear damping: This is probably what you want***. Linear damping applies a force backward that is proportional to speed. The slower the object is moving, the smaller the retarding force. Note that this technically means the speed will never reach zero, but it will quickly approach zero such that you can apply a check to see if speed < 1, set speed = 0.
Angular damping: This works just like linear damping, but for rotation.
***Note that "linear damping" is actually a better simulation of air drag than of skidding along the ground. Ground friction is best modeled as a constant force, but you will need to do a number of additional checks to make it completely accurate, and I'm not sure it is worth the effort and extra events for a game. To see the difference between friction and air drag in action, go to https://www.simbucket.com/simulation/rocket-sled/.