This is the 4936th most frequent Russian word.
комнату
The Russian word "комнату" means "room" (in the accusative case).
The word 'комнату' is in the accusative case and is the direct object of the verb 'вошёл', indicating the destination of the action.
Он вошёл в комнату.
He entered the room.
Here, 'комнату' is also in the accusative case and serves as the direct object of the verb 'убрал', showing the thing that was cleaned.
Я убрал комнату.
I cleaned the room.
In this case, 'комнату' again in the accusative case is the object being acted upon by the verb 'украсила', with the additional context of flowers as the means of decoration.