So here is what you need.
1: A vector image to screen print.
2: A blank screen
3: A sign squeegee, or credit card.
4: A vinyl decal or access to a vinyl cutter.
5: Masking/transfer tape.
Step 1: The image to decal
1: Find the image you want to screen print, and if necessary convert to a vector image.
(It will need to be vector due to the vinyl cutting stage only working with vectored images.)
2: Cut the image, or get it cut for you!
(its very important that you ask for it to be a negative of the image, or if your weeding the vinyl yourself you need to weed the line-work from the vinyl)
Step 2: Setting up the screen
Your decal will have a wax paper backing sheet and a transfer tape front, you need to peel off the wax backing sheet to expose the sticky vinyl.
Place the decal sticky side down on the screen and rub it all over with a credit card or sign squeegee.
Now peel off the layer of transfer tape to expose the no sticky side of your vinyl decal.