This is a one shot, also known as a 'monostable timer'.
When the timer is triggered by SW2 it will remain ON for a predetermined period set by the preset VR1. The preset varies the time ON from approx 1 sec to 120 seconds.
The timer is started by a normally open contact connected across SW2 this could be a push button switch, leaf switch, reed switch, etc.
This activates the relay and starts the timer. The relay will change state and remain in the new state for the timer period.
There is also a normally open Reset switch SW1 to reset the timer to OFF. The reset can be used at any time during the ON period
Supply Voltage 12v DC
Relay Specification
2 Changeover dry Contacts
Contact material:  AgNi (Au Clad)
Contact Rating:  2Amp 30vDC
Contact Rating:  1Amp 125vAC
Max Switch Power:  125VA / 60W