How do you wire up a Pir outside front door Light?

How do you wire up a pir light on the outside wall by the front door (without running it off a plug socket and without getting a qualified electrician in to do it as can't afford electricians fees sorry guys! and can you have a pull switch that would byp the pir sensor so that the light would stay on and once you turn the pull switch off returns it back to pir sensor uk electrical wiring system using a 20 amp 4 aperture junction box running the mains feed off an internal light ?