How do I load external SWF files into a Master SWF?

i've really been struggling for weeks to find the answer to a simple question. i'm trying to build my flash website and i cannot for the life of me find the action script 3.0 code for loading an external .swf into the blank master.swf. i have old projects that i referred to, even tried using the code and then changing the instance and file names, but it didn't work because it's an older version of as ( i don't even remember which.) see i want to have a blank master.swf and have it load the navi_menu.swf at all times, as well as load multiple content.swf as i navigate through the menu. can someone please offer me the code, or direct me to an up to date webpage that could explain this to me?