Install Belt to Pulley
Grab the timing belt and place it over the pulley of the stepper motor. The teeth in the belt should grab onto the teeth of the timing pulley.
Install Belt to Camera Mount
Work the timing belt into the notches of the camera mount. Press the belt into the slotted features of the camera mount to secure it in place.
Install Belt to Bearing
Grab the other end of the timing belt and work it on top of the radial ball bearing. Pull the belt and press it down so it grabs onto the ball bearing.
Install Bearing Cover
The bearing cover slides into the grove on the edge of the bearing mount. This rests in place and doesn't need any further securing. The tolerances will be loose or tight, depending on the printed part. That should not effect the performance.