We often listen to people from spanish-speaking movies saying "tú" a lot, but that is not the only way of talking to someone. For example, in Argentina, people say "vos". What is this difference about?

The difference relies in conjugation and usage. First, it is very important to mention that both are correct, and they are just different ways of speaking. Second, both are the second-person singular pronoun. "Tú" is used in Spain and most of Latin America, while "vos" is used in Argentina, Uruguay and Central America. Both of them are used in an informal context; speaking to friends, family or trusted individuals in general. If you are talking in a formal context (boss, elder person, etc), you use "usted".

Let´s use the 3 options.

1. You are intelligent / Vos sos inteligente / Tú eres inteligente / Usted es inteligente.
2. You are my bestfriend / Vos sos mi mejor amigo / Tú eres mi mejor amigo / Usted es mi mejor amigo.
3. Where are you from? / ¿De dónde sos vos? / ¿De dónde eres tú? / ¿De dónde es usted?.

The meaning doesn´t change at all, but the translation changes depending on the level of formality and the way of speaking.

Remember, neither is wrong!

If you have any questions about the usage just tell me and I'm happy to help!

Also, if you would like to know more about a particular topic, please don't hesitate to ask.

Good luck :)