A spear consists of a long shaft that has a sharp point at one end. You might use one to go spear fishing, but that's about it. Spears are no longer the weapon of choice.
Spear also refers to the action of impaling something or someone with a spear. “Odysseus blinded the Cyclops by jamming a huge spear into its eye.” In addition to the long-shafted, pointy spear that people throw, spear is the name for the sprout of a plant. In the vegetable world, separate stalks of asparagus are called spears.