Sure Colman... it's really fairly simply.
First, you can program the Fn button to do whatever you want. I have it set (at the moment) to go between Auto-Focus and Manual-Focus. However, I recently discovered that by being in S-AF+M Mode (single auto-focus + manual mode) works just as well. With a MF lens on, the AF won't even attempt to work, so I can just stay in S-AF+M Mode. Either way, the point is that you need to change the camera to be in S-AF+M Mode or MF Mode. Even without the Fn button, you can do it by hitting the back arrow/AF button.
Once you're in MF mode (however you got there) you just manually focus by turning the focus ring on the lens.
If you want to engage Focus-Assist (which took me some help to figure out), it's not hard at all.
Press the Info button until you see the green square. Now, if you hit the OK button it will magnify your view for easier manual focusing. Hit the OK button again, and it will go back to normal.
Also, if you hit the OK button to magnify, you can toggle between 7X and 10X magnification by turning the wheel (the bigger one).
With one of my M-lenses attached, I just leave it in the green-square/focus assist mode. Even when turning the camera off, it'll start back up in that mode. That's the easiest way to toggle focus-assist on and off as needed.
It all sounds more complicated than it is (when you write it down). Really, it's as simple as being in S-AF+M or MF mode, setting the Info button to green-square/focus assist mode, and leaving it there. Then all you have to do when you want to take a shot is raise the camera and manually focus, hitting the OK button with your thumb to toggle magnification as needed.
If you have any questions, let me know!
