I'm sharing some photos of my pillow making process. They are shots of what I figured out along the way. If you google search on piping you'll find lots of fine tutorials out there. I checked out about a dozen over the last week (and made some great friends along the way). I chose to make envelope pillows as well. Lots of great tips if you google that too.
1. Pin your piping as pictured to the front piece of your pillow. Raw edges facing out. I had previously drawn my seam line around the perimeter of the pillow. I just matched up the piping stitching to that line.
2. When you get to the point where you need to join the piping, you'll fit it as pictured covering with excess fabric.
4. I sewed the piping to the fabric front by keeping my zipper foot hugged up against the piping. Below is a picture of how I cared for where the piping meets.
5. Finished front of pillow with piping stitched on.
6. Lay the shortest back panel on first and stitch. The wider back panel goes on top. This way when you flip it inside out your envelope is in the middle.
7. Keep that zipper foot hugged up against the piping as you sandwich the two pieces together. Once done, push out the corners and flip the case inside out. Iron and then stuff your pillow form in.