Your is a possessive word that shows something belongs to or relates to the person you're talking to. When you say “your book,” you mean the book that belongs to them. When you ask “Is this your pencil?” you're asking if the pencil belongs to the person you're speaking to.

We use your constantly in conversation: “How was your day?” “What's your favorite color?” “Is that your dog?” It works for both physical things (your backpack, your bike) and non-physical things (your idea, your opinion, your turn).

Your stays the same whether you're talking to one person or many people. “What's your name?” works whether you're asking one new classmate or a whole group. This sometimes causes confusion, which is why people might say “you guys” or “y'all” to make it clear they mean multiple people, but your itself doesn't change.

Don't confuse your with you're, which is short for “you are.” A simple test: if you can replace it with “you are” in the sentence, use you're. If not, use your. “You're going to love your new teacher” uses both correctly.