One of the tails from the holder goes to the positive pole on the switch.
The other tails is soldered to the Box wire.
The second wire on the Box wire is then soldered to the negative pole.
When it’s all in place and working (always best to do a circuit test at this stage to make sure your wiring is correct) then the bulb holder needs to be hot glued into place.
You can use some small headed self tapping screws too, and just screw the bulb holder into the head.
Insert the bulb into the holder, and then place a blob of hot glue underneath the holder and press it into place. (keep it central). When that has dried, remove the bulb and give a liberal dose of hot glue around the holder to secure it in place.