Lay a drop cloth on adjacent to the area where you will be applying the stain.
Open and mix the deck stain. Pour it into a paint tray.
Dip the roller brush attached to the extender into the deck stain gently. Lift the roller and move it over the paint tray moguls. Continue gently dipping and rolling off the paint on the moguls until the roller brush is completely covered but not dripping. Roll the stain on the planks of the deck, rolling with the grain of the wood. If you have over-saturated your roller brush and you see runs or drips, simply roll over them quickly with a roller brush.