You do not create movieclips on the timeline using code, though you can create them and add them as children of something that has been manually placed in the timeline.
To create a MovieClip using code you use:
var mc:MovieClip = new MovieClip();
If you need to add an image, then however you intend to acquire the image, after it has been acquired, you add it to the MovieClip using:
where img is the instance of whatever form of object the image takes (Bitmap, Loader)
If you need to add a TextField to the MovieClip then you use:
var tf:TextField = new TextField();
and you can set up properties for the textfield such as the font and color and position as well after it has been instantiated (the first line).