Hi Gail, here's one way.
or you can cut out the fabric, leaving an extra 1/2-3/4" of fabric all around and use adhesive seam tape available at JoAnn's, Hobby Lobby, etc. to iron togethe to create seams. Here's a tutorial. https://www.youtube.com/watch?v=0WeR5ZtzSQ8
Stitch witchery or Velcro! Here are some cool sites.
here are many ideas/videos https://www.youtube.com/results?search_query=diy++no+sew++pillows
Braided edge is another no-sew idea.
This style of covering works best with fabric that does not fray.
The technique of Furoshoki, traditional Japanese folding of fabric for gift wrapping, can be applied on pillow forms as well. The effect can be especially attractive when double-sided fabric is used.