ti or tú?
tú means you, so what does ti mean'
Just to add a slight complication to what Matt said: there are a couple of prepositions that generally use the "tú" form rather than the "tí" form:
entre tú y yo
una persona como tú
hasta tú lo puedes hacer
(And of course con gives the form contigo.)
I was going to leave a comment, but it seems that Matt here answered su pregunta!
they both mean the same thing, but are used in different situations. you just have to realize when you are using a subject, prepositional, or object pronoun
tu is used as a subject pronoun while ti is used as a prepositional pronoun. also remember te, which is an object pronoun (for indirect, direct, and reflexive).
para ti -> for you
detras de ti -> behind you
contigo -> with you (notice how when you write 'con ti' it becomes contigo)
tú estas al gimnasio -> you are at the gym
¿de qué país eres tú? -> what country are you from?
ahora mismo no eres tú -> right now you aren't yourself (this one is different because there is no reflexive for ser)
te he dicho -> I've said to you, told you
¿te vas a dormir? -> are you going to sleep?
¡cuidate los nuevos gatitos! -> take care of your new kittens!
one thing to remember is that you don't often see tú because it is usually implied. for example, estás implies that it is the tú form of the verb, and you usually just see 'estás' instead of 'tú estás'
Tú is a personal pronoun used as the subject of a sentence or clause.
Ti is a personal pronoun used as an object of prepositions.