Place your completed puzzle front-side down. With a work board underneath the puzzle, place another work board over the top of the puzzle and secure the ends of the boards together before flipping it upside down.
Apply puzzle glue to the entire back surface of the puzzle. You may use a paint brush to help even out the application of glue. When it has dried, apply another layer of glue.
Take the back board of the frame that is specifically fitting to the length and width of your puzzle's measurements and place it on top of the dried puzzle's back.
Hold the work board and frame's back board together securely at the ends while you flip the puzzle.
Lift the work board off the puzzle, exposing its front side. Place the glass and frame on top of the puzzle. Securely holding all ends, flip the puzzle upside down.
Lift the frame's back board and tuck the puzzle's edges into the frame before securing the back board in place.