I don't understand how personal pronouns work like te, le, nos, os, les, le, lo, la, los las. Bear with me as English grammar was something I had trouble with. When I see a grammar mistake in English, sometimes I cannot tell you why it's wrong I just instictively know it's wrong.
Hi there. The pronouns are used in different ways:

- For replacing a noun/direct-object previously mentioned. For instance:

¿Quién tiene el libro? Who has the book?

Juan lo tiene. Juan has it.

Juan va a leerlo. Juan will read it.

- For indicating who receives the action of the direct-object. For example:

Carol compra un regalo para mí. Carol buys a gift for me.

Carol me compra un regalo. Carol buys me a gift.

I'm not a spanish teacher, but I can suggest you to check this page http://www.studyspanish.com/lessons/dopro1.htm with more information (and exercises!) about this topic. Check out the chapters 41 to 47, within the Unit Four, on the left column.

¡Buena suerte!
Man this is so difficult for me I am in the USA an I am trying to get ESL but I just went to school in Guatemala I not even finished meddle school! Not easy but I am getting there!