How to tell which wire to connect to a bayonett lamp connector

That's all there really is to it - white to white and black to black. If they are not color coded then the black wire should be connected to the pin at the bottom of the light socket.

This assumes your light is line voltage (120V in North America). If it is not line voltage then there should be a transformer somewhere in the fixture already.

Procedure

• Turn off power to the lighting circuit
• Test that power is off using a non-contact voltage detector (NCV) and/or Cat-II multimeter.
• If necessary to prevent cable chafing, fit a cable grommet to the backplate cable opening. (since the backplate may be heated by the lamp, you may need to look for a grommet that can be used in hot conditions)
• Strip the insulation from the ends of the live and neutral wires.
• To the screw attach an earth wire (bare or green/yellow in UK)
• In the hole above the embossed "L" push the live wire (brown in UK).
• In the hole above the embossed "N" push the neutral wire (blue in UK).

Notes

• The push-fit connections are unusual in UK fittings and are intended for solid-core wires (not stranded)
• The holes connected to the metal strip are not for powering the light.
• The fitting appears to be designed for use with a separate junction box fitted in the ceiling.

• Live wires from a light-switch sometimes have the wrong colour insulation but are marked with red tape (indicating switched-live).

• Typical wiring for a ceiling lighting fitting in the UK is as shown below

Note that this image does not show the strain relief that must be present on the hanging cable. Fittings with exposed metal parts will need a protective earth connection. The one you have looks like it particularly needs this!