For this step you will need your spacers, bound envelopes, glue and large binder clips.
Run a bead of glue along the stitches of your bound envelopes (picture 1). Align your spacer with the edge of the envelope and apply firm pressure. Carefully remove any leaked glue with your finger tip and wipe away on your jeans (or a towel, etc.). Repeat on the other side. Secure the spacers to the envelopes with the binder clips (picture 2) and allow to dry.