Step 4: Sewing layers together
I use the freemotion sewing technique, I am not going to go into detail on how to do this, if you want to learn this you can go here and take a look at Leah Day's video on starting with freemotion sewing. She is amazing and shows you that you don't need an expensive machine to do this. As she does it so well, no point in me trying to fumble through it.
Or you could use your normal stitches on your machine, it will take a bit of stopping, starting, turning etc.. it is possible to do it that way. or again, you could hand sew it.
Once sewn you then remove the stabiliser, as it is soluble you can either rinse it off under a running tap or just carefully tear it away. I do the tearing method as you don't have to wait for the fabric to dry before the next step. Trim all long threads from both sides of the porthole.