For a long time, attaching zippers were daunting to me.
When I first started sewing, I avoided any projects involving zippers until it was
no longer possible to avoid learning how to do it anymore.
I usually get the 110cm length which comes with 4 zip fasteners.
First, pull all the 4 fasteners out and open the zip.
Next, attach the zipper foot and use only one strip of zipper,
sew around the bag openning with the needle on the right.
Sew the zip all around the bag openning, stop just before you reach
the starting point. Leave about 1-2cm gap.
Adjust the zipper foot so the needle is now on the left,
sew around the bag openning again.
Not only have you managed to attach the zipper but you've also
topstitched and created a professional look to your bag.
*it might be a bit tricky the first time*
Cut the access zip and push it inwards.