Sync allows you to essentially copy the contents of an existing step, to a new one.
SYNC BLOCKS button will be available when two blocks have been selected.
SOURCE AND TARGET need to be selected in order by clicking them with the Shift-button pressed.
SYNC OPTIONS have two different options.
Sync Positions: Use this when you want to copy all the location attributes from objects, to these same objects in another step. Note, this does not copy the objects themselves!
Sync ICSOS: Use this when you want to copy all the Object data (SO's, locations, camera, animations) to another step. It will create a carbon copy. Note, if you have "new" objects in the target step, that do not have the same id-number as in the source, they will not be overwritten.