turn off
Separable
Stop an appliance, light or tap
Turn the tap off when you brush your teeth.
Separable
The object can go between the verb and the particle: turn the light off, or turn off the light. When the object is a pronoun it must go in the middle: turn it off, never turn off it.
The particle: off
This verb belongs to the group ‘switching and shutting off’.
Others in the group: switch off, shut off.
Practise it
Add it to your daily practice or see every verb with off.
Further reading: turn off on Wiktionary (CC BY-SA).