If you have a specific panel in mind, go to that fabric manufacturer's web site. They often have a sample quilt made from that panel. You can also google panel quilts which should give you some ideas. Printed panels are different sizes. They usually (but not always) are about 42", which is the width of the fabric. From there they vary by width. If you are not using a pattern specifically for that panel, you may need to do some math to make the surround come out even. if you go to a quilt shop, they often have coordinating fabrics, sometimes with smaller panels. What specifically are you finding confusing?