Details: Now, time to make a shirt. At last! I strongly recommend using 100% cotton shirts, as opposed to cotton/polyester blends. But eh, I've done it on cotton/poly. It just doesn't look as good, and you can't heat-set it as strongly since you have to use a cooler iron.
So! On the top side of your screen, put down some masking tape to cover the gaps around the edges of the screen. This will keep your ink from gooshing up into the edges of the screen and causing an unholy mess. Position the screen over the shirt in whatever place you wish to put it. It's a good idea to put a sheet of paper or thin cardboard inside the shirt to make sure the ink doesn't go all the way through to the back of the shirt. And do your actual screening with a hard surface underneath so you get a nice, crisp image.
Time for ye olde flood fill. To do a flood fill, take a big glop of fabric-grade silkscreen ink, more than it seems like you'll need, and put it in a fat line at one end of the screen. Take the squeegee, and in one smooth motion, drag the ink lightly across the screen. Now, take the squeegee and drag it down over the flood fill, applying strong pressure, such that the ink squishes through the negative design and onto the shirt. To make sure you get a good layer of color, do three or four passes. Take the screen off and observe your newly-created shirt. (Sorry I don't have a photo of this step in process, but my hands were covered in ink.) Add ink as needed to keep your shirt-pulling run going.
When you're done making shirts, rinse your screen out immediately so the ink doesn't dry in there and clog it up (you can save any excess ink for later use). When the shirts have dried, take your iron, set it to cotton, and place a piece of paper over the design. Iron for about three to five minutes (depending on fabric thickness) to heat-set. It's good to turn the shirt inside-out and iron the back of the design as well.
For information on the best way to keep your new shirt looking good, please see the
t-shirt FAQ.