You can purchase resist at Hobby Lobby and probably Michael's. Some crafters use Elmer's Blue Gel glue.
These shirts are usually done with Silk Screen. You'll need a frame with a silk or polyester organza screen. To get your artwork on the screen so it can be reproduced you cut a stencil or use photo-sensitive emulsion. You use acrylic or oil based ink to print your artwork onto your fabric. You will also need a rubber squeege. You can get a basic silk screen kit or a fancy, expensive deluxe kit at art supply stores like Michael's or the Hobby Lobby. You can also order online from Dick Blick or Utrecht or other silkscreen speciality retailers http://www.silkscreeningsupplies.com/
Cheap and dirty method is make-it-yourself from recycled materials http://www.instructables.com/id/Screen-Printing%3A-Cheap,-Dirty,-and-At-Home/
There are so many ways to silk screen, so many levels of equipment, and many different ways to make a stencil, I am not going to try to give you a how-to here or even suggest some You Tube videos (of which there are many) My suggestion is to go to the library and get some books. You can also check with organizations in your area that offer arts or enrichment classes. Silk screen is an enjoyable hobby that many people enjoy.
There are also iron-on transfers that allow you to print out your design from your inkjet printer onto the transfer and then iron it onto your shirt. These are sold in several different grades from cheaper ones that only print on white fabric to pricer ones that will print on dark fabric as well. I have only used the less expensive ones, and the designs have been kind of light. http://www.staples.com/Avery-3271-Inkjet-Light-Fabric-Transfer-Paper-8-1-2-inch-x/product_355125?cid=PS:GooglePLAs:355125&KPID=355125