A garden hose spigot that drips or runs constantly is almost always a worn washer or packing issue. This takes under 20 minutes.
Turn off the indoor shutoff valve. Open the spigot to release pressure. Remove the handle, then use an adjustable wrench to loosen and remove the packing nut counterclockwise. Pull the stem straight out.
Inspect the rubber washer at the end of the stem. If cracked, flattened, or worn, pop it off and replace it with a matching size from your assortment kit.
Wrap the stem threads with plumber's tape, reinsert the stem, and tighten the packing nut snugly. Reattach the handle. Turn the water back on slowly and test for leaks.