Assuming you want to cool down the room and there is 1 window: Open the window in the room and open the door to the room. Ideally open a window somewhere else

Assuming you want to cool down the room and there is 1 window: Open the window in the room and open the door to the room. Ideally open a window somewhere else in the building and make sure there is a potential airflow from that other window to the one in your room. Place the fan in the window of the room you want to cool down and let it blow outwards. Alternatively you can place the fan in the same way in that other window you opened.