It depends on what of kind of wood. If it is new deck, you could use clear stain. If it is old deck, use semi-transparent or solid stain. You need to wash the deck and let it dry before apply the stain. You can buy a special deck stain applicator from HW store. Don't paint if it is going to rain in 24 hours. Don't paint if the tempeture drop telow 10 degree.