A few weeks ago I prepared a design on a screen using screen filler as an example for a class I was teaching about screenprinting to a group of secondary school students.
The group had been studying textile designs from different cultures, so I took my pattern idea from a piece of African fabric.
I put the piece of paper under the screen and copied the design onto it with a pencil. Then I painted my design onto the outside of the screen (the flat side) using screen drawing fluid.
When the drawing fluid was dry, I spooned some screen filler onto the screen and swiped it across the whole screen (and over the drawing fluid) with a squeegee. Don't swipe the screen filler over too many times as you don't want to rub the drawing fluid away.
I waited for the screen filler to dry (overnight) then washed out the drawing fluid by spraying a hose from the inside of the screen (the back of the drawing fluid - and behind the screen filler, as the screen filler does not wash out with cold water).
Then I washed the front of the screen as well, to wash off any bits of screen filler that had come off in front of the drawing fluid, and that's it - when the screen dries, it's ready to print. This is one way to screen print at home without needing expensive/bulky equipment (i.e. an exposure unit).