I don't remember the details of how shares are split between creator and curator and I believe it is quite a complicated calculation. As for the 3 options: I think you may be asking about the options available when writing a post? If that is the case, then there seems to be a choice of allocating ALL of your earnings to Steem Power, allocating your earnings 50/50 between Steem Power and steem (the default setting), and not taking any earnings at all.

This video is rather old and some things have changed, but it does a decent job of explaining things: