Why I cant attached animation to my script ?

I have script and animation, when I write
myanimation = GetComponent <Animation>();
I cant add animation to script, it not attach to my script in the inspector. When I write
myanimation = GetComponent<AnimationClip>();and changed type to AnimationClip, I can attached it, but it doesn’t working, because I don’t know some way how play this animation.
I’ll tried use Animator, but it doesn’t attached too. Animator attached only if I write
myanimator = GetComponent <RuntimeAnimatorController>();. I don’t know this is unity bug (I have similar problem on Unity 4.5) or I make something wrong.
Please help me.

try AddComponent