Step 1 (and all the steps):
Identify areas that need rust treatment, wear down with steel wool, and then paint!
The basic idea behind treating your van for rust is to find nearly-exposed, exposed, and rusted metal, clean it with the steel wool and then paint it to make it rust-resistant for all of the adventures your van will carry you through!
First scrape those places (nearly-exposed, exposed and rusted) with the steel wool, sweep out the mess, spray your first layer of rust oleum (the metal primer), wait the instructed time (it lists the time to dry on the can), and then add the final coat (the protective enamel)!
There you have it, you’ve done your first van project!