Add Symbol in Scene with Actionscript

you can use addChild() to add objects that you create in the ide and were once on stage (so they have an instance name) or that you created with actionscript.

if it's a library symbol, you'll need to assign a linkage id and create an instance using that id (using the new constructor) and then apply addChild() to the instance:

var mc:MC = new MC();  // where you have a symbol in the library with linkage id = MC

addChild(mc);