You're is short for "you are" and your shows ownership. If you're getting them mixed up, your secret is safe with us. Better yet, here's help! It's your secret. And now you're about to know more. See?
"You're a shining star" = "you are a shining star." You're is a contraction for "you are," and that apostrophe goes where the "a" fell out. When parents get mad, they say the whole thing: "You are not going anywhere, bud!" But when you're in love, like in these songs, you keep it simple:
"You're the one that I want, oo, oo, oooo, honey." (Grease)
"I guess you're just what I needed." (The Cars)
"You're so vain." (Carly Simon)
Your is the possessive form of the second person pronoun, "you." Say that ten times fast. It's all about ownership with your. Without that apostrophe, the word your points or describes something that belongs to the person being spoken to, as in "your dirty socks." (Pick them up!) It's a key ingredient in "your mama" jokes and these two songs:
"Your Cheating Heart." (Hank Williams)
"Your mama don't dance and your daddy don't rock and roll," (Loggins and Messina)
Although the old-fashioned word yore as in "the past" sounds just like those other two, it's less likely to pop up. You're goes before something you're (!) doing or being (you're falling into the lake) and your goes in front of something you own, like your leopard-print bathing suit.