What does "tu" mean?
Wait wait wait.
As Rey wrote
Tu (without accent) = your - ¿Dónde está tu libro? Where is your book?
Tú (with an accent) = you - ¡Tú eres genial! You're great!
Note: Tú is a subject pronoun, and can usually be omitted since it will be tied into the conjugation and usually clear.
Yo - Soy
Tú - Eres
él/ella/usted - Es
Te = object pronoun - ¿Te gusta el béisbol? Do you like baseball? or Is baseball pleasing to you?
Just go to the site I left you.
This is the place to go for unit by unit introductions to the Spanish language. Then you can intermediately visit this site to test out what you've learned. Especially when the chat is back running. Buena suerta. (of course the grammar guides on this site are great also for furthering what you learn.)
Tu means your. For example, a conjugation of tu would be: ¿Te gusta montar a Caballo? means "Do you like to ride horses?"
Tu eres bienvenido al foro.
( This tu is not necessary, I've put it in to demonstrate the meaning).