The aim of citySquare is to match up the tiles from the tray on the right on the grid as best as is possible in a given amount of time. Points are awarded for completed cities (the somewhat poorly drawn orange bits) and roads. They are however taken away if the city or road is incomplete.
Also note that scoring is skewed to give more points to large cities, so you should really be trying to make your cities as large as possible within the time limit. Finally, ensure that all of your tiles match up, and that any tiles touching the edge of the grid are grass, any invalid ignored for scoring purposes, don't waste those tiles!