Tú is a subject pronoun therefore always use tú as the subject of a sentence. Notice the accent mark on the u. Ti is used as the object of a prepostion. Ti is used after spanish prepositions such as: a, de, para, etc. There are some exceptions, of course. Tú tienes suerte. (You're lucky/have luck) Tu vecino ha comprado un regalo PARA ti. (your neighbor has bought a gift for you). Esta galleta te pertenece A ti. (this cookie belongs to you.) or Esta es tu galleta. (this is your cookie, tu, no accent mark). For more details and if you really want to study deeply this subject, then you can visit this link: http://spanish.about.com/od/pronouns/a/subject_pron.htm

I'm going to give you some examples: Tú eres de los Estados Unidos - You (informal) are from the United States of America Tú eres muy buena chica. - You are really good girl. So, "tú" means you - informal Now... TI can mean: 1. Something belongs to "you - infomal" or that something is for you. Éste beso es para tí - This kiss is for you (means, the kiss belongs to you) I did not expect this from you - No lo esperaba de tí 2. If someone goes to you (moving) Voy por tí - I am coming to pick you up. Voy hacia ti para que estemos juntos. - I am going to your place so we can be together. I hope it was helpful to you. If you have any futher questions, feel free to ask me.

Tu ..use like you ...and ti is an typical accent from south of brazil

Tú means you, it's usually paired up with a verb. Tú aprendes -> (You are learning) Ti is used when you are talking about something that belongs to you, or is for you. Este regalo es para ti -> (This gift is for you).

Tú o usted, is a subject like (you). Tú eres inteligente.You are clever. Él es listo.He´s smart.