Summarize this article:

To connect the pocket, pin it onto the front of the body piece so that the pocket is centered. Make sure that the body piece is turned right side out and the right side of the pocket is facing out as well. Pin along the flat edges of the pocket and leave the curved edges unpinned. Then, attach the pocket to the front of the body piece by sewing along the pinned edges.  Make sure that you only sew the pocket to the top layer of fabric. You can skip this if you do not wish to have a pocket.

Summary:
Pin and sew the pocket onto the front of the body piece.