You want to know what "dot filtering" is, or how to apply it, or both?
Dot filtering is a weathering technique using small dots of color to modulate (or change) the underlying color, be it a base coat or camo scheme. Most people use either artists oils or enamels since they have longer drying times and therefore blend together better than acrylics. The colors you use for dots will depend on the color you're trying to filter. The basic colors used are primary colors like red, french blue, white, etc. Sometimes you will see offsetting dots used with a multicolor camo scheme like the German WWII Ambush scheme, where dots of dark yellow (basecoat) are used in the brown part of the camo, and the brown color might be used to filter the green, etc.
The key is to do small sections at a time, so the dots don't have time to start setting up and you end up with lots of little circles where the paint dots started. A general rule of thumb is to use a protective coat between your base coats and the filter. I don't know what type of paints you use, or plan to use, but oils and enamels are more aggressive than acrylics, which is why most use a sealing coat between the two.
Hope this helps some.