The caps (and posts) have a long prong that stick out, while the sockets and studs each have a center hole. The prong is poked through the fabric and then comes up through the hole of a socket or stud. The cap and the socket are one set, while the stud and post are one set. The instructions on how to attach the snaps are as follows.
1 Place your capped post, post up, on your setting anvil.
2 Place the forward side leather piece wrong side facing up, so that the post pushes through the hole.
3 Put the socket over the cap.
4 Put the punch on the socket and hit the punch using the hammer.
5 Repeat this process for the remaining stud and post to the backward side leather.
6 Finished picture.