Joining knitted pieces

I don’t understand how to join knitted pieces together. I’ve watched the videos on this website and I’ve got several books but I’m not joining a sleeve or seam in a garment. I made the snail shell purse pictured on this website under “Getting started”. I got the pattern from cheapknittingpatterns.com because the link no longer links to the pattern. I’m now finished with all three pieces and the next instructions is to “coil the sides to look like a shell” which I have done and sew in place. I don’t know how to sew it in place and I can’t find any instructions that I feel is the right way to do it. I assume it means to use yarn??? And the large yard needle but I can’t figure out how to do it that it wouldn’t affect the appearance of the piece. After the sides are sewn into place you have to sew the handle on. Can anyone help me?:ick:

You would still use the mattress stitch that’s demonstrated because you’re going to seam two edges together. Doesn’t matter if they’re on a sweater or a purse where you coil the strip around. It may help to pin the edges together in a coil so they stay put, while you get started.

Thank you so much!