Not sure this is the right forum so prepare to be moved, however:
Managed is basically flying what's in the box (Nav to waypoints, Cruise/Descent speeds determined by the FMGC etc)
Selected is 'selected/chosen' by the pilot. (Headings, Speeds etc)
To get open climb, simply pull the altitude knob will drop it out of CLB mode to give you OP CLB (with climb power - not MCT) - if you want MCT you have to select it via the thrust lever gate.
There's plenty more to it than just that - I'm sure someone else will go into more detail but I've been up since 0430 (!) - ah the glamour
