The 'Look At' dialog is used to point an object at another object in the scene. This relies on the object having it's 'forward' direction in the +Z direction (as a camera does). If the object faces the other way, the 'Flip' command should be used in the object's properties to get the correct direction.
Settings
Look At Object - Click to select the object that you want to 'look at'. This will set the position automatically.
Track Object - Check this and the object will be looked at every frame.
Track Flip - Flips the direction of the look at.