Well that makes a big difference. It is fun, it is creative, and there are so many different ways to do it, though none of them are cheap. Each requires computer, printer, software, heat press and/or flash dryer etc.
For a quick lesson in learning each kind go to youtube and search for videos on the different kinds that I'll list here for you. That will give you an idea of what you're in for.
screen printing, inkjet heat transfers, laser heat transfers, plastisol transfers, foil transfers, vinyl transfers, rhinestones, embroidery, sublimation, direct to garment (DTG). I think that's most of them.
For screen printing supplies go to
Screen Printing Supplies, Screen Printing Equipment & Screen Printing Kits. For sublimation supplies go to
Sublimation Printing, Unisub Blanks, Supplies, Inks, Video Tips and Tricks, Transfer Paper, Heat Presses, Direct to Garment. For the rest browse through the vendors on the left of this screen. You will also need a vendor or reseller's license to buy shirts wholesale. If you want to make anything for children you will have to make sure that you are in compliance with federal consumer safety laws regarding products for children under 12.
In the main forum here you will find different areas dedicated to specific types of printing. That's where you'll find the experts hanging out at that can answer your questions.