the window
The word 'la fenêtre' is used to refer to a window in French. It is a feminine noun, so it takes 'la' before it. For example, 'Je regarde par la fenêtre' means 'I am looking out the window'.
I open the window to ventilate the room.
This sentence is active indicative in the present. It shows the action of the speaker opening the window to let fresh air in the room.
He looks out the window, thoughtful.
This sentence shows someone observing the outside world through the window. The comma is used to link two independent phrases, with the second explaining the mood during the action.
She broke the window by accident.
This sentence is in the past tense using the auxiliary 'avoir' and expressing an accidental act of breaking the window.