Animation layer problem

Hello

Please can anyone help me cause i haven't found an issu for my problem. I have a rotate animation wich is supposed to be played when i rotate my player, but when i rotate my player the animation doesn't work and my idle animation continue to play like nothing happen. I have tried to make the rotate animation in layer1, but in this case the rotate animation replace the idle and i can't play any other animation Here is my code

 if(Input.GetButton("Horizontal"))
         {
         myTransform.Rotate(0, Input.GetAxis("Horizontal")*Time.deltaTime*speedRotation,0);
             if(animation.IsPlaying("idle"))
             {
             animation.CrossFade("rotation");
                }                               
         }
     else
     {    
         animation.CrossFade("idle");    
     }
         

thank you

PS: can anyone explain me the difference between the animation.weight and the animation.layer, i have read the documentation but i haven't understood yet