This is a climbing technique, it is hard to describe but I shall try. Your body is face on to the rock.
Imagine a small ledge for you left hand. If you are facing a keyboard then the handhold is at the left edge of the keyboard or further to the left (the point is that the hand hold is not in line with your centre of mass but is away from it in the same direction as the hand you are holding the hold with). The hold is at shoulder heigth or higher. Now in your mind rotate the hold through 90 degrees clockwise. Your fingers are pressing against the hold and you are pusing away from your body.
The force is coming down through your shoulder blade and you are leaning your weight onto your shoulder blade. Your left elbow is high and pointing to the left. This is a gaston. It is named after a famous french climber born in 1921 called Gaston Rebuffat.