In order to prepare an image (design, graphics, illustration, photography) for screen printing, one need to understand a little bit how this method works.
Now note that the image is transmitted to the network by means of a photographic emulsion, a type of light-sensitive liquid that is applied in a thin layer on the grid. When the emulsion has finished drying completely on the grid it works as follows: When it encounters light it becomes difficult and becomes waterproof when it is kept in a dark area it easily falls under water. Therefore, in order to create the image on the mesh the image area should be blocked so no light can get through. You do that by printing the image in black-opaque color with a simple home printer on a film. Using a dedicated light table or projector to expose the screen to light with the black image printed film on it. After it exposes the image will wash in water: the result on the mesh is negative of your image.
* This is suitable for everyone and is specifically intended for participants in my screen printing workshop. See what this is about.