We utilise a very used brush , something that we can toss after this application. Cheap craft brushes for these specific tasks can be obtained at Wally World or Michael's or your fav Brick and Mortar Craft Store.
Using the surface primer , blot some on and stipple it onto the area needing the texture. Try not to do an area to large for this stuff dries fast. Then sprinkle on some baking soda , Let is set for a minute or two and blow off with your air brush or lungs.
Areas that will accumulate a large amount of crud add some layers of the previous steps.
Don't forget areas that are easily forgotten, like the undersides of fenders .
Let all this work sit for a time before progressing to the primer coat, which will be covered next.