I have found two types of shutter. Most have removable lensboards that clip into the front of the shutter. The shutter itself is either built into the front standard or is screwed to another board which is then attached to the front standard. My Lancaster Instantograph uses the latter method:

There are some that don't have a separate lensboard and seem to be one solid unit. These are made to slip over the end of the lens.

To set the speed you need to turn the brass knob at the other end of the shaft to which the speed dial is attached. In the picture above you can see the brass knob just above the hole where the string comes out. The little bent spring next to it sits in a notch in the knob and prevents the knob turning. You will need to gently compress the spring so that the knob is free to turn and then you can change the speed.

To change from Time to Instant you need to move the lever over. There is a little piece of bent brass that engages with a prong on the bottom of the lever that prevents this. You need to gently pull the brass upwards and the lever will then be free to slide over.