This is a single channel (on / off) universal switch that may be used with any Infra Red remote control using 36-38kHz. (This is a very common remote handset frequency). In place of IR1 a TSOP1738 receiver may be used.
Any "button" of any remote control may be used to work this universal switch. The button must be pressed for about one and a half seconds (determined by R3 and C2) before the relay will operate. The circuit will remain in this state (latched) until reset. To reset, any button is pressed on the remote handset and held for a short duration.
For example, if you were watching TV, you could press and hold any button on the TV remote to trigger the circuit. In order not to change channel, you could press the button of the channel you are watching. You can connect anything to the relay, for example a lamp, but make sure that the relay contacts can handle the rated voltage and current.