You need to attach the male magnetic snaps to the triangular cardboard pieces before gluing them to the leather, but the rectangular cardboard on the left must be glued to the leather before attaching the snaps.

Before gluing, push the female snap tabs through the leather exterior and the rectangular cardboard to make sure everything is positioned properly. Then apply glue to both surfaces. When they are slightly tacky but not wet, very carefully and lightly put the cardboard pieces in place. Once the two tacky surfaces touch it's extremely difficult to adjust their position, so just be careful and use a steady hand... Once it's in place press down and bend the snap tabs over the washers to fix in place.

You will have installed thee female snaps on the case's exterior, and two male snaps on the top and bottom triangles. The third triangle glued to the exterior leather does NOT have a male snap, because there will be a pocket for your protractor above it. The third male snap piece needs to be attached to the pocket cover (i.e. the smaller triangle which is not yet glued to the leather exterior).

Please note: if you will be using a thicker leather to cover these side flaps, you will need to glue that leather piece to the top and bottom cardboard pieces, attach the snaps through the leather and the cardboard, then glue the interior leather and cardboard to the exterior leather. You can't hide the male snap under thick leather, because the center won't stick out enough to allow a good grip.