Sociolinguistics 4, Exercise 1: Joos's styles

A wedding vow                         frozen: fixed wording, like a pledge
A lecture to a hall                   formal: one-way communication,
                                      like presentations
A teacher explaining to a pupil       consultative: two-way, background is
                                      explained (the source's own example)
Two friends joking                    casual: talk among friends, with slang
                                      and ellipsis
A parent whispering to a child        intimate: private talk among family,
                                      relying on intonation and shared words

Source: Wikipedia, Register (sociolinguistics). The wedding-vow, lecture and
parent examples are my illustrations of the source's descriptions.