What they do? Those rotate an element clockwise around the x/y/z-axis, while a negative value would rotate it in the opposite direction.
 
     
     
    
     transform:rotateX(0deg)
    transform:rotateX(0deg)
     
     transform:rotateX(180deg)
    transform:rotateX(180deg)
    
     transform:rotateY(0deg)
    transform:rotateY(0deg)
     
     transform:rotatey(180deg)
    transform:rotatey(180deg)
     transform:rotateZ(0deg)
    transform:rotateZ(0deg)
     
     transform:rotateZ(50deg)
    transform:rotateZ(50deg)