Single button footswitches are usually designed to take you back and forth between presets or channels on the amp that you’re connecting it to. Usually you have to get the footswitch that is compatible with your amp, but there are also generic options that will work with most amps.
When you’re not looking to add too many different effects, just to switch back and forth while playing, all you need is a single button that you can hit with your foot.
The Fender 1-Button FootSwitch is designed to work with many vintage and new Fender amplifiers.
The Orange FS-1 1-Button Footswitch gives you more control over the Orange amps Terror Series.