Control external SWF from parent SWF

Hi,
I am studying yet. so I am using Macromedia Flash 8. I’ve created a swf file as (main project.swf) and Loaded a external swf using loader component. the file is main_slide. Now I want send a command or data to project file, from loaded main_slide.

please someone help me to do this.

(my English may bad)

THANK YOU!:flower: