you go out the door!
you have to go to counterfeit island
You get the key from the person next to the lab
You take it back to counterfeit Island and use it on the door of the house.
If you are referring to the keycard in Poptropica Counterfeit Island, you use it to unlock a door in the secret lair, which can be found in the countryside. It is locked so you have to find a key.
you go to the countryside on counterfeit and then the key will open the door to the building that is there.
you do nothing
The curator of the Museum Fantastique summons you to Early Poptropica and gives you a key, which fits the cottage door.
In the Clown Shop.
Sneak out and hide behind statues go through the storage room door and you will be by the dock.
you go to main street with your ticket and you give it to the lady next to the Gate door that is slightly open.
nothing