Whether in Java, or in the real World, classes are groupings of objects.
Cars are a good example.
They are all different, but have a common characteristic that allows you and I to call them by the same generic name of car. You drive, park and service your car in much the same way as everyone else. Except that your car has it's own particular way of doing these things. So you can say that the class of cars has a common method for driving, parking and so on, but that this method can only be provided as a concept at the generic car level. It can only be properly described for each particular car model.