To yank is to pull or move suddenly and sharply. You might reach for a pan on the stove and then yank your hand away when you realize the handle is hot.
Your little sister might yank at your arm to get your attention, while a bully might yank your hair just to be mean. In both cases, they're tugging abruptly, and you can call the pull itself a yank. Don't confuse this noun with the yank that serves as a slightly offensive nickname for Americans, or even more specifically, for New Englanders. Dutch settlers in then New Amsterdam first used this word to insult English colonists in Connecticut.