Choose a name for your movie clip object. Pick a name that reflects the function or shape of the movie clip object. The ame should contain only letters, numbers, an underscore or a dollar sign character. Don't begin the movie clip name with a number, and don't use a movie clip name that is a reserved keyword for other AS3 functions (see Resources). Names that don't follow any of these conventions will generate a coding error, and your AS3 program will not work.
Examine the other variable names you are using in your AS3 program. Ensure that the name you pick for your movie clip object is not the same as any other variable name you are already using (AS3 is case sensitive, and the variable name "MARK" is not same variable name as "MaRK").
Use the following general syntax to declare an empty movie clip object.
var <movie clip name>: MovieClip = new MovieClip();
where "var" is the AS3 variable keyword needed to declare a variable and "<movie clip name>" is the name of the movie clip you have chosen for your movie clip.
"MovieClip" is the AS3 keyword needed to declare a movie clip variable (object).
Start the Flash program. Click "Flash File (ActionScript 3.0)" from the splash window to create a new file for an AS3 Flash animation project.
Select "Actions" from the "Window" menu on the main Flash menu bar to open the ActionScript 3 editor. Position your mouse cursor on the first line of the ActionScript 3 editor. Click your mouse button and type in the following code to declare an empty movie clip named "movingCar."
var movingCar: MovieClip = new MovieClip();
Click the "Check Syntax" blue check mark icon at the top of ActionScript 3 editor's toolbar to have Flash check that the syntax for the empty movie clip declaration is correct. Observe that the Flash dialog box appears and says, "The script contains no errors."