Since the leak typically occurs in the hot water line the leak will usually be noted by the floor getting warmer at the leak location. By going back to the hot water tank you will find the hot water line that will have a starting point where the copper line connects to the tank and outward from there into the house. In order to make the repair a new section of copper tubing is attached to the water line before the leak, bypasses the leak and connects again after the leak.
When done correctly the work will be almost hidden and the repair will be complete. This will produce a long time solution to the problem at the point of the leak repair and should be done by a person who professionally performs this type of work. There should be a very short time with the