Typing code in a Movie Clip

I am new to Adobe Flash. I am trying to make a small game and I am having trouble adding a code to an “object” or MC. So, I drew a circle using the ellipse tool, I selected the black cursor, clicked on the circle, F8 - made it into a Movie Clip. Now, I right-click it and select “Actions” and it says “Current selection cannot have actions applied to it.” What am I doing wrong?

How do I start typing code in a Movie Clip?


EDIT: lol, I just figured it out…it was because I didn’t name the instance…

Another question though. What is the difference between this._x and _root._x ?