Hi Millie, this article gives step by step instructions on how to paint a screen door - https://www.doityourself.com/stry/painting-a-metal-screen-door-stepbystep
Here's a video tutorial: https://www.youtube.com/watch?v=GP-LME_kAmM&list=PL0YXfoIwvbZsNmIJDgC2vm1l7RJjG6CrP
Hi Millie - here is another good tutorial: https://thesweetestdigs.com/the-diy-files-painting-a-screen-door/
Remove any peeling paint, clean with denatured alcohol, tape off with paper on the screen. Cover hardware as well. Now you are ready to prime & paint. Make sure you get a paint that is for doors.