The Smokescreen spell creates a cloud of smoke to obscure vision.
Although, the incantation of this spell is not mentioned on Pottermore, a recently released trailer of the Pottermore PlayStation Home project reveals that the incantation, in fact, is "Fumos". During the Book Herding scene in the trailer, one of the players steps on a round icon, displaying the wand gesture of the spell and clearly shouts "Fumos".Also,with the new update,spell's name is confirmed to be Fumos,as it can be used in dueling now.
Pottermore Playstation Home
In the Book Herding, stepping on the Smokescreen spell icon will cloud the other players in a haze of smoke for 10 seconds. This makes it difficult for them to see what they are doing exactly.
In the Wizard Duel, casting the Smokescreen spell also clouds the other player in a haze of smoke. They start coughing and need a moment to regain their composure, giving the caster time to move behind a train bench or prepare their next move.