A Free Form Role Playing Game, commonly known as a FFRPG, is a role playing game that uses no dice. Although alternative methods for combat may be used in their place, it tends to vary from game to game.
The best advice would be to read all the information you can find about that particular game from their webpages, message boards, or any other sources they may have available.
If you're still not sure what is going on, then start asking questions. Most people don't mind answering honest questions for people who may be unfamiliar with the game, and have an honest interest in learning.
FFRPG is a game where players create characters, and then together with other players they build stories, adventures, etc.
The creation of the stories, adventures, plots, etc. takes place over a period of time, through interactive writing between the players.
One player creates and posts a starting point for the story,
then another player creates and posts another piece of the story in a reply to that one,
then possibly another player creates and posts a reply to the second player,
or the first player may even create and post a reply to the second player, or third player, and so on.
The options are endless, and through their combined efforts they tell a tale to hopefully entertain themselves, and others as well.
This is the heart of Free Form Role Playing Games, the creativeness of those who participate in them.
What do you need to play? A good imagination, and a willingness to have fun:)