To attach the clamp you first need to slide the nut into the plastic housing as shown here until the centre of the nut lines up with the hole:
Then hold the clamp as tight as possible around the handlebar and start the pinch bolt into the thread of the captive nut
(taking care not to cross thread it) and then tighten the bolt securely with a suitable screwdriver or allen key etc. making sure that the display is in the correct position and angled to give the best display.
If your battery does not have an integrated On/Off switch, then the battery
must be unplugged and left disconnected when the bike is not in use.
If the battery is not turned Off or disconnected, it will be slowly discharged by the controller and the LED battery gauge on the throttle while the bike is not being used.
The red button on the throttle is typically used to turn a suitable battery voltage LED headlight On and Off.
Alan