This can be used in two ways.
It can be mainly a listening exercise. The students listen to the teacher describe what is in the space 'There is a bear sleeping on the sofa' and they draw in that detail. After adding the 10 details they can then write sentences about their room.
Alternately they can make pairs with other students and create the details themselves. Either play rock scissors paper and the loser tells the winner a detail they can add to the space. Or be cooperative and share details. In the later case I'd have student A say a detail and both add it then student B say a detail and both add it.
Once they've added 10 details they can write sentences about the space.
An additional activity could be naming things. After adding ten details they can name the things. For example 'there is a bear sleeping on the sofa' is followed up with 'The bear sleeping on the sofa is Henry'.
The pictures used for the room worksheet were taken from a worksheet posted here. I can't remember where it is now though.