Put the coupler onto the shaft.

Make sure you can see thru the holes (it could be off 180 degrees and a little crooked), then put on the bolt, lock washer, and lock nut. Tighten.

Couple it to the motor, tightening down the set screw.

Tighten the motor mount bolts.

Bolt the bearing closest to the motor to the mount with a washer, a lock washer, and a lock nut. Tighten these down.