"Sich" is used for reflexive actions, i.e. when the subject and object of an action are the same, in the 3rd person: – He washes himself. = Er wäscht sich. – They wash themselves. = Sie waschen sich. Likewise for prepositions: – He talks about himself. = Er spricht über sich. The pronoun systems in German and English are slightly different there. In English you always have a couple "X"/"X-self" of object pronouns for non-reflexive and reflexive use, in German the pronouns only differ in the 3rd person. For example: – He washes ME. / I wash MYSELF. = Er wäscht MICH. / Ich wasche MICH. – I wash HIM. / He washes HIMSELF. = Ich wasche IHN. / Er wäscht SICH. "Selbst" is used (for all persons, not just 3rd) to emphasize that someone does something oneself (but not *to* oneself as above), personally, on one's own: – I'm coming myself. = Ich komme selbst. – He writes the letter himself. = Er schreibt den Brief selbst.