"This flower is for you."
Translation:Esta flor es para ti.
In Spanish and English, there are subject pronouns and object pronouns.
"Tú" is the Spanish second person singular familiar form SUBJECT pronoun and, by definition, can be used as a sentence's subject (Tú pensa, asi tú exísta). "Tí" is an OBJECT pronoun and can be used as the object of a preposition as in "para tí" (for you).
Because "tú" is a subject pronoun, it cannot be used where a Spanish object pronoun, such as "tí," is used. Similarly, because "tí" is an object pronoun, it can act as the subject of a prepositional phrase. There are three types of object pronouns, and this wealth of Spanish pronouns means that there are many more Spanish pronouns than English pronouns used for direct and indirect objects.