Plug a hot glue gun into a wall outlet and insert a glue stick into the gun. The glue can warm up as you prepare your work surface and gather your materials.
Place an unframed sheet of mirror on your work surface. Measure the length and the width of the mirror with a ruler.
Measure the length and the width of the frame. You need a frame that is exactly the same dimensions as your mirror sheet.
Squeeze a line of glue along the edges of the mirror. Press the frame onto the mirror, making sure to line up the sides, while the glue is still soft. Allow the glue to dry.