Unfortunately no hints are given in the game to help you find the secrets. You'll either have to find them both for yourself or look below.
The secret doorway is hidden on the beach to the right of the sandcastle with the flag with KMM written on it. Just bridge over the flag and walk to the right of the beach.
Saving all of the ducks in this secret level is not easy at all. Whether or not it can actually be done is unknown by me. I've never actually done it. But here are some hints to help you save as many as possible. Notice the switch at the rockets. Do not let a green duck touch this otherwise most of the ducks cannot be saved. Always make your ducks line up behind the green duck into the rocket. Also when you take ducks from the side of the screen be careful as some of them may fall off the bottom. Finally, when you only have a leader duck left, you can flick the switch for some extra points.
At the bottom right hand corner of the screen there is a dark blue lego brick where the secret doorway is hidden. Take your green duck over there by bridging a way down from all of the other dark blue bricks.
A rubbish secret level if I do say so myself. You can earn over 5000 points by shooting the rocket and teleporters and letting the aliens fall off the screen. Just shoot any aliens that get trapped in the centre. If you want to save the duck, it is possible, but very hard. You must shoot any alien that gets in your way taking care not to destroy any teleporters. Hey, I didn't say it was easy.
A Flying Doctor's SonProduction