Design (check tutorial)
Print or heat transfer vinyl decal
Heat source( I currently use a clamshell heat press)
And obviously a shirt lol
Other things
Teflon sheet to go on top of vinyl.
If using sublimation prints, use non waxed and non bleached butcher paper. Also make sure you protect the other side of your shirt or bag or whatever by putting cardstock inside of it for ink seeping through.
A T-shirt ruler for better design placement, many places have them and you can probably find and print one.
If you have a roll of vinyl you'll want a vinyl cutter that can cut it into 12*12 inch sheets.
I'll add to this if I can figure out anything else I'm forgetting which I probably am knowing me. I will also try to find some links that you can buy directly from without having to search up stuff at a later point.