In regular (ie, unmodded) civ 4 there are no ranged units (except air units). All ground combat is "melee". Archers get some first strikes, which are like "extra" combat rounds where only the first striking unit has a chance to do damage.
Archer units are mostly used as defense. You can hold strong points with them, they get large bonuses if they defend cities or hill and especially cities on hills. They are unsuited for attacking, but of course it comes up now and then.