I need to know when to use nosotros, nosotras, usted, tu, es, eres, and more basic words like the, which, who, what, how. P.S. I really want to learn Spanish!
Yo, tú, usted, él, ella, nosotros, nosotras, ellos, and ellas are subject pronouns. They are the equivalent of the English I, you, he, she, it, we, they words, and they can be the subject of a sentence. SpanishDict's guide to Subject Pronouns is a good place to start.
Soy, eres, es, somos, son are conjugations of one of Spanish's "to be" verbs. They are like am, are, is in English. More info here: http://www.wordreference.com/conj/EsVerbs.aspx?v=ser Don't be intimidated by this humongous chart. Just look at the top left column, Indicative Present.