This seems to be necessary. it's = it is. its = possessive they're = They are. their = possessive there indicates location, as in "over there." To is a preposition. (A sentence should never end with a preposition.) Too is used in place of "in addition," "also," or "as well," et cetera and also indicates that something is to an excessive or marked degree, as in "too little," "too many," or "too much." Who is used as a subject. Whom is used as an object. For example: Correct: Who has the biggest penis? Incorrect: Who shall I show my penis to? Correct: To whom shall I show my penis? I could keep going, but those are some of the more important points.