Just like other items with moving parts, switches wear out over time and, unfortunately, they can’t be repaired, so they must be replaced.
If you are new to your home, you might find switches that don’t seem to operate anything. In those cases, look for a wall receptacle that appears to have been installed upside down. This could indicate that the receptacle has been wired to be controlled by a light switch. “Switched” outlets can be used to control a table lamp via the switch rather than using the on/off control that is part of the lamp.