what are fans? and what do they do? annd how do you get them?

There are one hundred and twenty of fans hidden in the game and some of them are very well hidden.
To "collect" a fan you have to shoot it to blow it up.
Your reward for collecting all one hundred and twenty fans is two new weapons to select at the weapon selection screen. The Laser Gun can be used only by Batou, and fires extremely powerful explosive laser beams. The Napalm Launcher can be used by both Motoko and Batou, and is basically an extremely high-powered high-explosive rocket launcher. Both will end up killing you a lot if you're not very careful with their blast radii.
It can be though to find them all, but it's possible
I think you have to have beaten the game once to make them appear

(being sarcastic)
http://www.handyhippo.co.uk/images/products/p694i.jpg
thats what a fan looks like.
they are for target practice.
blow em up ^)^

Yeah that's how they look