Hi Josh,
A chairman game, is ran using an in game editor, i can only speak of FM 2013 where i used FMRTE (which was a little awkward as you couldn't create new transfers, whether it be staff or player changes, you could only edit current transfers, which affected the computer-assisted team transfers as you effectively stop a transfer which was already a done deal), I haven't used SI GAMES version , so can't comment, there.
The game idea is that you act as the chairman on the game via a forum/thread, where one or a group of people simulate the savegame, manage the forum and make all the editor changes, after being involved in transfer negotiations and basically acting like the FA for all activity, whilst updating the threads/forums.
There will be a Chairman assigned to each team in that division and then they have the power to sign new management/staff to run their club on a day to day basis and crucially on the sideline. The manager will then be able to make transfers for the club using the budgets you have allocated him, and impose his style of football onto the team.
Also, as Chairman you are able to sign players from other chairmans involved (and you will get a bargain!!), also you can sign foriegn players and domestic players (not run by a chairman) but bare in mind that rules will be set upto you and basically you will have limitations based on your club rep, managers rep and various other details, giving it a more realistic approach.
During the transfer windows and after any update, you are expected to contribute towards the story, by posting your latest teams news, rumours and chairman press conferences etc. (again check the rules of the thread as you may be required to get these authorised prior to posting for example, transfer confirmations.
Basically, that's how it works throughout the duration of the game. I ran a couple last year until the save game crashed and burned, thanks to my **** laptop.
Will be looking into launching a new one this year when i have found a savegame/team i can stick at.
Take a look at mine:-
Story Thread
Rules and Sign Up
Hope this helped,
bornexplorer88