Habbo Duckets are a free virtual currency that you can earn just by playing Habbo. There are many ways to earn them such as logging in daily, being active, completing certain Achievements and any other fun surprises that the Habbo Staff can come up with.

Awesome! How do I earn Duckets?
Logging in daily. The more you're active the more you will receive.
Spending time on Habbo.
Completing Achievements.
Completing Achievements in the Habbo Citizenship track.

What can I spend my Duckets on?
Furniture in the Shop.
Avatar Effects in the Shop.
Visibility with a Room Event.

Additionally!
Furniture in the Shop, can also be purchased using combinations of Duckets, Habbo Exchange and Habbo Diamonds.