A file system is implemented by subclassing the llfuse.Operations class and implementing the various request handlers. An instance of the this class must then be passed to llfuse.init to mount the file system. To enter the request handling loop, run llfuse.main. This function will return when the file system should be unmounted again, which is done by calling llfuse.close.
It is probably a good idea to look at the Example File System as well.