That looks nice. Constraining isn't really that hard although like most things it often needs tweaking to get it right. In the cloth room after you've set up the collision go down a little further and click on edit constrained group. It's where the arrow in the screen shot I've attached is pointing. The group editor will popup when you click that. By default you'll have a selection tool, so basically you can just drag around the area you want to 'pin' in place. The red dots that will appear on your item are the constrained area. You can remove them by clicking on the minus sign and selecting. Or if you click on the box next to the plus and minus you can get a pencil tool to be more exact with.
The important thing to remember is that you aren't really 'pinning' the fabric in place. It's actually more like adding glue to that section of the fabric. When it collides against something, the areas with glue will stick, and won't move away from whatever they've stuck to.
Hope that helps.
Thank you so much!
