Right Bob! You know that it has ended when you accomplish the stated aim; lighting the two torches on the top right circular thing. It also comes up with 'The End' in big letters that fill the screen.
Have a go by all means but do not read the bit below in italics if you don't want it spoiled. You've been warned. I didn't write this myself by the way.
Open the hatch on the right above the upwards-pointing arrow, and click the arrow to get a little man to operate your cannon. Open the window of the house in the bottom left (so the inhabitants can hear the bell when it rings) and nake sure the arrow suspended above it is pointing right (so they know which way to run when the time comes). This all becomes important later.
Fire your first rock upwards at the bell, but - WAIT - as it hits the bell you need to click on the see-saw/spear thing, so that it swivels and ends up pointing upwards on the left. If you don't do this the rock will trap it in the position it started in. As the bell rings, the house door in the bottom left should open.
Angle your cannon down and fire the second rock to knock the plank into place for the bridge. The next two things you fire are grenades, and they're a complete red herring. You need to get rid of them without destroying anything, so fire them down and click on the bridge just before they hit it. It'll bounce and knock them upwards to explode harmlessly in mid-air. Fire your last projectile down so it'll bounce into the cave and the man can open the door.
Click on your cannon-eer again and he'll get inside it. Get another man from the up-arrow and have him fire upward - your first chap should land by the bell. Click on him and he'll move the scaffolding. Click on the see-saw to have it revert to its original position, and keep clicking on the bell till it falls off. This should catapult the rock down to clear the landmine below. With that done, click on the open house door and a chap will come out and have a clear path to light the firtst torch for you.
If you click on the bloke in the cave at the bottom he'll run to light the second torch, but a dog (or man on a bike with slicing wheels, I'm not sure) will drop out of the '!' box and kill him. What you need to do is start him running, and then (timing) open the window above him - the chap inside will slam it shut, and the ceiling will cave in and kill the dog, (or man on a bike with slicing wheels, as applicable).
And there you have it!