Use the latex paint to cover all the space that you don't want to print. It is very important to make sure that you have covered all of this negative space. To be sure, look through the screen at a light to try to detect any places you've missed. If you traced your design, use a small brush for tight spots.
Let the paint dry, this could take an hour to five hours, depending on how much paint you have used. When it is dry, test your screen by laying it on a blank piece of paper and brushing over the entire screen with thin watercolor paint. The image on your piece of paper is what will appear on your clothing. Fix any mistakes by adding more paint and testing again before you print.(People commonly use Mod Podge for this step, which is not a practical solution. Why use latex paint instead of Mod Podge?)
Next, apply the ink.