How does flash use the as2.0 language to control the loading of video clip 1 when the mouse clicks on the stage, and then the loading of video clip 2 when clicked again?

Since you can use the as2.0 language, you should be able to do basic programming. I will not write the specific code. I will give you an idea for your reference:

Create a button frame And a loading frame

Create a stage-sized button in the button frame. When making the button, select the "click" frame (transparent button), and then place it on the top layer

Then add the counter (i++;) under the button and goto to the loading frame;

Load the video clip name + i in the loading frame and then goto back to the button frame.

This is basically it. now;