you can also pick up a guy, move a space, pick up another guy, move a space, then drop off for an amphibious assault in the same turn
you can also pick up a guy, move 2 spaces, pick up another guy and then drop off for an amphibious assault in the same turn
etc etc
you can not however, do a battle, then pick up and drop off into an amphibious assault, as that would take two turns since all battles are done at the same time and ends the combat movement phase.
krieg: lets say you have a british troop in Karelia, and you wish to transport him into germany for an assault on berlin. The germans have a surface warship in the baltic sea, say a destroyer. You have at least a transport and surface warship/airplanes. Can you move into the baltic sea, pick up from karelia then drop off in germany, conditional on winning the sea battle?