A plow is a large tool used for farming. A farmer drives or pulls a plow across a field to prepare it for planting.
The large blades of a plow break up the earth, cutting and turning it so it's loose and ready to be planted with seeds. When you operate a plow, you can say that you plow. Boats can plow through water, too — in fact, anything that moves forcibly forward also plows: a car plows through traffic, and figuratively, a student plows through her homework.