Place the cable in the terminals and tighten then back in the plug.
You must have the correct cable in the correct terminal
The earth is always at the top (green and yellow stripey)
The live (brown) is always by the fuse.
The neutral (blue) is therefore the only terminal left
Make sure the terminals are tight and there is no bare wire showing.
Tighten up the strain relief so it clamps the outer insulation.
Screw the plug back together.