For a 14" x 14" silk screen, you'll need a 14" x 16" piece of 3/4" plywood or particle board; about six feet of 1 x 2 pine; two loose-pin hinges with screws; two wing nuts, bolts and washers; a piece of silk screen fabric (available at good craft stores) about 18" square; duct tape; and a loaded staple gun.
First, assemble the silk screen frame from pieces of the 1 x 2 pine. Then staple the fabric to the frame, stretching it tight as you go. Trim away any excess fabric.
Next, cover the edges of the frame with duct tape, allowing the tape to extend onto the fabric about half an inch around both the top and the bottom of the square (it prevents ink from seeping under the fabric and onto the frame.)
Finally, cut the base so that it's as wide as the frame and two inches longer. Bolt a section of 1 x 2 to the edge of the base along the base's width. Place the frame on the base and attach it to the 1 x 2 bar with pin hinges.
And that's how to make a silk screen.