Some footswitches have a 1/4-inch monaural "telephone plug" connector, the same as the output connector on a conventional electric guitar.
Other footswitches have the same physical plug size but in the TRS (tip-ring-sleeve) configuration.
Other footswitches use a five-pin MIDI connector.
Still others use any of a number of different physical connector plugs. The wiring of the connection mechanism may be proprietary to the manufacturer. These may even include digital connectors.
You must identify the exact make and model of your amplifier, and you must find the instruction manual for the amplifier, which will explain the exact specifications of the footswitches that can be used with it. Then you can determine whether you must use a particular model of footswitch sold by the manufacturer of the amplifier, or if you can use another brand of footswitch made by a different manufacturer.