Hand pump sprayers are inexpensive compared to sprayers that require an air compressor. However, the pressure created by the hand pump is not as even or controllable as a compressor-based sprayer's. This makes hand pump sprayers a bit unwieldy if you are a novice painter but with a little practice, you can create a relatively even paint coating. The process can be very messy, so remove any objects you don't want painted from the area and use dust sheets and masking tape to cover any remaining surfaces.
Pour latex paint into a mixing bucket through a metal strainer to remove any lumps or impurities.
Thin the paint with water according to the instructions on the paint can. Most thinnable paints will have a paint-to-water ratio for sprayers listed right on the can.
Stir your paint and water thoroughly and then pour paint into the sprayer's paint bottle up to the manufacturer's recommended fill line.
Pump up the sprayer until the pump mechanism feels stiff and resistant. The pump is usually a handle at the top of the sprayer that you pull out and push in to pump in air.
Set up a large piece of cardboard so it is the same orientation as the surface you want to spray (vertical for walls or lying flat for floors).
Practice spraying the cardboard in sweeping motions while standing with the nozzle a suitable distance away from the paintable surface.
Pause and re-pump the sprayer when you feel the pressure start to drop off or notice a change in the way it is spraying.
Continue practicing with cardboard until you are comfortable with your control of the sprayer and its performance.
Spray the surface you want to paint in the same manner you used with the cardboard.
Clean the nozzle thoroughly with water when you are finished, or any time the paint seems to create blockage.
Sprayers vary, so practice standing at different distances from your cardboard until you find a distance that gives you an effective, controllable spray.