Which aspect are you curious about? The overall workflow of setting up the server-side architecture? Information on tools that can generate SWFs? Or information on the SWF format itself?
As for tools, here are a few options off the top of my head:
- The Flex SDK (i.e. mxmlc) will compile a pure AS3 project with embedded assets. If you've got reasonable control over the server, and don't mind a relatively heavyweight approach, that's probably the most "supported" way to go.
- SWFMill (http://www.swfmill.org) has its own XML format for generating SWFs and importing assets. It's not quite up-to-date on newer SWF formats, but that may not matter depending on the requirements.
- www.swftools.org has a few things that may be useful.
- haxe.org has several options for generating SWFs.
If your question is about generating the format from scratch, all those projects are open-source, and personally, I've found the haxe sources to be the easiest reading. The library you want is http://code.google.com/p/hxformat/. Taking a look at the swf format spec might be helpful as well: www.adobe.com/devnet/swf/.
Or were you looking for more step-by-step detail?
(note: sorry for the lack of active hyperlinks, apparently the system doesn't believe I'm human yet :)