There are no warlocks. Pagan is a broader category. There are many different types of pagans. Witches are one of the most popular groups. I tell my students now that Pagan is to Wicca as Christian is to Catholic.
Witches do magic and spells.
Simply they are opening up to natural forces and energies in the universe. They are tapping their own psychic abilities. They are attuning to the energy around them. Spells are like focused prayers. You are asking for a specific event.