Simplest thing first:
Set the little lever that is around the shutter release button to "O".
Next up:
Remove the dark slide from the magazine, and press the shutter release button.
If that doesn't help, press the pre release below the wind crank (up), and press the release button.
If still no luck, insert the darkslide (getting it all the way in may be a bit hard), remove the magazine, and look through the rear shutter.
If the rear shutter doors are still closed, push the bottom one in (it hinges at the bottom. Will not do any harm).
You will see a small light greyish screw sitting below the lens. Using a small screw drive, gently try to turn it clockwise.
At this stage, still only prodding the screw, not really turning it, you may already hear a click, and the camera will be 'free' again. (You then still have to complete the cycle: press the release button - usually does nothing - let it go again, and wind the camera usingthe wind crank).
If it does not go click immediately, proceed to turn the screw clockwise until it locks. You're turning against the tension of the various springs powering the camera, so it will be a bit hard to turn the screw. Yet no real great force is needed, so if it doesn't go, do not attempt to use great force anyway!!!
If the screw truns, you will notice that the shutter will open too.
After that, after the screw has locked, take out the screwdriver, and release and wind the camera. If it locks up again, same procedure, but take the lens off after the screw has locked. You can then try the camera alone. If it still jams, you are out of luck: no more photography until the camera is seen too. So no assigned shot using that camera tonight.