Repairing small and large leaks was just addressed but because leaking is one of the biggest concerns for garden hoses, another similar question presents itself. This time, it is referencing what happens when your hose is leaking from either of the two end fittings (or both). While this is not the guaranteed issue, there is a high probability that it is leaking because there is a bad gasket. If you notice that it is not even there anymore or is warped horribly (look for the rubber washer), it is time to get a new one.
Granted you have some sort of flat tools, such as a flat-head screwdriver, you can remove the current gasket by popping it out. Once the old one has been removed, install the new rubber washer and secure it by pushing it down. Make sure the washer does not drop on its own as that indicates it is not secure.