Steps to connect a flex to a light bulb holder.
Switch off the mains supply. If the flex is already connected to the ceiling rose, remove the fuse for the lighting circuit you are working on.
Prepare the end of the flex that is going to attache to the bulbholder, see Preparing the flex for connection for details. Unscrew the upper cover of the bulbholder to reveal the screw terminals.
Place the flex through the upper cover and then place the blue neutral conductor into one of the screw terminals and tighten it. Next place the brown live conductor into the other terminal and tighten it.
There are usually lugs or grooves around which the two conductors must go to prevent strain on them. If the bulbholder or lampshade is metal then an earth wire will be required. Screw back the upper cover making the bulbholder ready for use.