Look at any example that you can find, self explanatory.
I think the main feature is that you can use a higher color palette and what above was said. (colors in .frm files are represented on 8 bit, with reservations to some special index, that is used to animate them, like the fire in barrels, or green slime pools.)
To view .frm animations easily try this tool: http://fodev.net/forum/index.php/topic,29877.0.html
- install java and use the top link, the exe files have been removed from dropbox. - It does not view .fofrm animations, I forgot to finish that part hehe, but you can export normal frm files into image files which the .fofrm files are composed of, maybe that helps you.
You can find more info on .fofrm files on the Russian websites, you might need to translate the pages though, but worth it, I found it somewhere the specification, but lost the link, sorry.http://docs.fonline.ru/page_format_fofrm.html