It's not really that complex, though i guess it is if you've only ever used digital.
The ring with B, 1, 2, 5, 10, 25, 50, 100, 250, 500 are shutter speeds, B is bulb mode, 1 is 1 second the rest are fractions of a second i.e. 1/2, 1/5, 1/100 etc.
The lever below the lens will select the aperture, f/4.5 to f/22 in this case.
The lever with the small round knob on it above the lens just behind the shutter speed ring is there to cock the shutter. This concept is rather alien to most, but essentially the shutter won't fire until you cock it. Just push it into place and you'll see when the shutter fires it moves back to it's original position so you can cock it again. The shutter release is on the top of the camera with Isolette's, the other button on the top of the camera should be for opening the front with you fold the camera up.
The little brass socket next to cocking lever is called a PC sync socket and it's so you can use a flash with the camera, amazingly because this camera has a leaf shutter it can use flash at all speeds, even 1/500th, most DSLR's can't even do that.
Most people didn't guess the focus back in the day they bought an accessory rangefinder that went in the accessory shoe on the top of the camera so they could get the distance right, you can get a cheap Watameter finder for under 20 quid, i have 2 myself. Some more info on accessory rangefinder here
Rangefinder (device)
Also the Camera-wiki.org page for the Isolette is much better than the old camerapedia one,
http://camera-wiki.org/wiki/Isolette, all the main contributors for camerapedia switched to working on camera-wiki after camerapedia sold out to wikia. Also try looking at the
Isolette group on flickr for a good idea of what the images taken with it look like.