In British English, it's often called a "zip," while in North American English, it's a "zipper." Both refer to the same thing.
They prevent "corner dips" and ensure the top edge of your bag is straight.
Fold a small fabric square, slide the zipper end inside, and stitch across. 🛠️ Essential Tools & Materials
If you're struggling, you can use heat-activated bonding or double-sided tape to position the zipper before you ever touch the sewing machine.