I don't consider myself much of a sewer, but there are some things that are so easy to make, even a novice like me can figure them out. For example, pillow shams. I like to make them with an overlapping opening in the back so they're easy to remove and wash. This is how I do it.
Start with the measurements of the pillow form. Cut one piece for the front, including the seam allowance. Cut 2 pieces for the back that will overlap enough to allow the pillow to be inserted but still close flat.
Sew a hem down both sides of the back pieces. This will become the edges of the overlapping pieces. Make sense so far?
Overlap those 2 sewn pieces and pin them right sides together even with the third piece (the front).
Sew all the way around and turn right side out. You could stop here, but I like to create a flat edging on my shams so I make the pillow case bigger and then top stitch to make the decorative edge. I know....I'm confusing myself too.
I use painters tape as a guide, so I know where to sew to create the decorative edge.
Sew all the way around and remove the tape.
See the difference?