First make sure the rifle is empty then remove the upper from the lower receiver.
Remove stock handguards.
Insert the front portion of the upper handguard with the “T” markings on top under the handguard cap. Pull the delta ring back until it’s resting on the handguard.
Put the lower half on the same way then snap both halves into place under the delta ring.
Unscrew the knob on the light clamp then squeeze it to snap the light onto the side rail of the handguard. If you are right handed mount to the left side, if you are left handed mount to the right side.
Tighten the screw to secure the clamp.
The switch on the side is so you can use the pressure switch so the light turns on when you press it and off when you release, or to make it stay on steadily when the pressure switch is hit then released.
To keep the light from turning on when not in use move the safety block over the pressure switch.