It's a little hard to explain, but I'm gonna try give you a basic rules (in spanish grammar like english there are exceptions).
Tú=You (when you are the person who do the action) (accentuated "ú")
For example: Tú eres grande. [You are big]. Tú comes pescado [You eat fish]. Tú juegas al baloncesto [You play basketball]... Usually "Tú" is omitted -> Eres grande; Comes pescado; Juegas al baloncesto
Tu=your (unaccented "u")
For example: Es tu coche [It is your car]. Tu perro es marrón [Your dog is brown]...
"Te" and "Ti" are used when "you" is the reciver of the action. "Te" goes before the verb; and "Ti" goes after verb + preposition (preposition different "a")
For example "Te": Te veo [I see you], Te quiero [I love you], Te odio [I hate you], Te necesito [I need you]...
For example "Ti": Esto es para ti [This is for you], (Ellos) marcharon sin ti [They go away without you]
Extra points :)
With you= Contigo. (Yo) fui al cine contigo [I went to the cinema with you ]
Yours=Tuyo. Este lápiz es tuyo [This pencil is yours ]
I'd hope that helps you, and sorry for my bad english.