Ian,
When you fly a circuit at an airfield, you fly around the runway in a rectangle shape with the runway making up one side of the rectangle. Thus you take off, flying into wind, ie-the wind on the day is going over your wings from front to back. Next you turn onto the 'crosswind leg' where the wind is coming at you from the side and you are making the top 'side' of your rectangle. Next you turn and fly the 'downwind leg' which means the wind is blowing you from behind and you are flying parallel to the runway you took off from, but in the oposite direction to which you took off. Once past the end of this runway you turn 'base leg' where again the wind is coming at you from the side, and on this leg you set up your aircraft to land. When you are ready, you turn onto 'Final' and there infront of you (like in the movies etc) is your runway, awaiting your landing.
Hope this helps,
SB
