To really appreciate the Forbidden City, you need a map. There is one posted near one of the gates, but it is in Chinese. I would suggest trying to search on the internet for one.
The Forbidden city was, of course, the home of the Emperor. It was built during the Ming dynasty, starting in 1406. It took about 14 years to complete. It is really quite large, about 2 miles north-south and 1 mile east-west. You enter it from Tiananmen gate, which faces south toward Tiananmen square. Actually, Tiananmen gate doesn't open into the city itself, but only to a sort of pre-courtyard that has some small parks and temples. You are not inside the actual city until you cross the moat and pass through the Meridian Gate. You can find the Meridian Gate on a map by looking for the moat and finding the upside-down U-shaped gate in the middle of the southern side of the moat. In the photograph of the map in the city, the Meridian Gate is at the very bottom (this map doesn't include Tiananmen gate at all). Proceeding north, you cross the Golden Stream, then encounter the Gate of Supreme Harmony. Passing through this, still going north, you enter the main courtyard, the Sea of Flagstones. At the northern side of the Sea is the Hall of Supreme Harmony, which is the largest hall in the city.