As its name suggests, this position is square of the wicket on the leg side.
You will even have the pleasure of the second umpire's company - you'll generally be standing very close to him.
Alertness is the name of the game because your job will be taking sharp catches and moving in for the quick singles.
There are a few variations in this position:
Deep square leg is back on the boundary, while at backward square you will be standing slightly behind the line of the wicket.
Short leg is a position usually given to the youngest member of the fielding side.
It's the unfortunate honour of standing just yards from the bat on the leg-side.
Reactions have to be very sharp, and it is generally advised that the fielder wears a helmet, box and shin guards.