You'd is a contraction, meaning a shortened combination of two words: “you” and “would” or “you” and “had.” English speakers use contractions constantly in everyday speech and informal writing to sound more natural and conversational.

When it combines “you” and “would,” it expresses what might happen or what someone should do. A teacher might say, “You'd enjoy that book if you gave it a chance,” meaning “you would enjoy it.” A friend might warn, “You'd better hurry or we'll miss the bus.”

When it combines “you” and “had,” it refers to something that already happened. For example: “You'd already left when I arrived” means “you had already left.” Or someone might say, “You'd finished your homework before dinner,” meaning “you had finished.”

The apostrophe shows where letters were removed when the two words merged. In formal writing like essays or business letters, people typically write out “you would” or “you had” in full. But in stories, dialogue, text messages, and casual writing, contractions like you'd make the language flow naturally, just as people actually speak.