Direct Object Pronouns

I learned that direct objects answers the questions of "whom" and "what".  I also learned that when you are using a direct object noun that is referring to a person, you must put an "a" in front.  If it isn't a person then you don't have to put an "a" in front of it.  Also, in Direct Object Pronouns you use me, te, lo, and la in the singular form.  In plural form, you use nos, os, los,  and las.