What's the difference between animation and animator ?

In many scripts i tried there are properties like walk speed or animation clip and more. But when using them it's not doing anything not effecting at all on the character. If i change the speed property or if i'm adding to the Animation clip HumandoidWalk. If i want for example to make my ThirdPersonController to walk not move but to walk with the walking animation then i have to go to the Window > Animator create a new empty State and use in it with HumandoidWalk if i set it to default all characters will start walking automatic when running the game and will walk with the animation. If i'm making the new state in the animator default then i will need in a script for specific character to use the Play("Walk") to make walk when running the game. But i see in some places many use animation or _animation with Play("Walk") but i'm using in scripts Animator or _animator with the Play("Walk") so i wonder What's the difference between animation and animator ? In the animation window i can change/create new animations and in the animator window i decide what action like walk idle crouch ?