In 3 axis machining, work piece is fixed on the table & table has been given movements in X & Y direction and Tool only moves in Z direction.
But in the case of 5 axis machining, work piece & tool are allowed to do movements relative to each other in directions other than standard X, Y & Z. This makes possible the machining of under cuts.
Following video shows the 5 axis machining. Unigraphics Nx has been used for this.