To tow something is to drag or pull it, the way a truck will tow your car away if you park it illegally.
A boat can tow a smaller boat behind it, and a person can even tow another person: "I had to tow my little brother down the hall by his arm to get him to leave the party." You can use tow as a noun as well: "My car won't start. Can I get a tow to the gas station?" Sometimes the chain or rope that's used to tow something is also called a tow.