on the left as one faces it; viewer-left
Used to specify the left side from the point of view of someone facing the object, stage, picture, building, etc.; this may differ from the object's own left side.
The reception desk is on the left as you face the entrance.
The person on the left as you look at the photo is my older brother.
左 simply means 'left', but 向かって左 explicitly specifies the viewer's left, which can differ from the object's own left side.
Transparent phrase formed from 向かって, the te-form of 向かう meaning 'facing toward,' plus 左 'left': literally 'left when facing it.'