Create your Flash sig and publish it as a .gif file.  Remember Flash is vector graphics so some gradients when published as a .gif loose that sharp color change.  Find a place on the Internet to host your sig.  This could be your ISP, a free sig hosting service (like www.yoursighost.com), or include it on a home page on one of the free services.  Finally go to your profile and add the link to where you hosted it. Every board seems to use a slightly different syntex but tipically an example would look someting like:

{img}http://www.yoursighost.com/MySig.gif{/img} -- replace the { } with [ ] in your profile.

  Let me know if you need me to be more specific than that.

Well, start out by selecting the "Text" option and type in the text you want in your sig.  Then try "insert" and "effects" and try some of them out.  Click "play" to see your work.  You can add and delete effects.  Jump in and try it...