Extreme Beginner Scripting Question

Hey, I am very very new to both Unity and Javascript so please bear with me with how simple my question is.

I am just trying to figure out the basics of how this works so I want a "cube" object i created to move up a little when I press the "Space" button.

I came up with this so far (my understanding is noted with // so whoever will respond can tell me if im correct)

     function Update () {      //every moment
 
 if (Input.GetButtonDown("Jump"))   //if Space bar is pressed down
 
     transform.position = Vector3.up;   //move the position of the object up along the z axis
 }

obviously it doesn't work any help is very appreciated