It looks like a lot of steps but really you’re just sewing the two fabrics together, sewing a bunch of button holes along the top, and then hemming the bottom and the sides!
First make your fabric the right size. With right sides together sew your top pieces of fabric together along the short sides so you have one long piece of fabric using a 1/2 seam allowance (mine was 16 x 71).
Sew your bottom fabric right sides together along the long edge with a 1/2 seam allowance. At this point I had a mermaid piece that was 73.5 x 71 inches
Finish the seams with a serger or using a zig zag stitch to keep it from unraveling if you wash it or if you have particularly finicky fabric (you can skip this step if you want it to be even faster).
Iron your top fabric in half WRONG sides together. So the pretty side of your fabric is facing out. With mine I now had a folded piece that was 8 x 71 inches.
Serge or sew the two unfinished edges at the same time to the right side of the top edge of the bottom fabric. Finish the edge if desired. When you lift up the top edge you should have a shower curtain just without the holes for the curtain loops.
Finally put in the holes for your curtain loops. Count how many curtain loops you have and then 1 inch from the folded top edge of you curtain mark spots to make your buttonholes. You can do math but I thought it was easier just to fold the curtain. If you are a perfectionist get your ruler out.
Sew and cut a button hole going vertically for each spot you want a curtain loop. If you don’t know how to sew a button hole just check out youtube or your machine manual it’s really a lot easier than most people think. I will try and post a tutorial for one soon. But I know google can help you out right now if you don’t want to wait for me ;)
Now go hang your curtain (yes I know it’s not done) you don’t have to put it on all the loops. You just want to be able to figure out the right length for the hem and make sure nothing looks off with the width. Pin your the bottom edge up so it’s your desired length. Remove it from the bathroom and then sew the hem.
Finally fold under both sides by 1/2 inch and hem them you’re good to go!