1st - Don't know exactly. I suspect a thin 'key' is inserted into the gap at the bottom and this separates the latch from the padlock hasp and opens the lock. I haven't seen such a lock before however so don't take this as anything other than speculation. I expect these were used more like the modern day zip-tie 'locks', in that did not provide much security but could have highlighted that the object it secured closed had been tampered with. Perhaps they were used to secure the tops of postal mail bags to ensure the contents had not been tampered with?
2nd - Possibly a lever lock, or a warded lock - both opened by various methods, the cheapest being wires - stickied threads will give you some idea.
3rd - I believe that this is a warded padlock, opened easily if so - see the stickied thread about these.
4th - TuBAR lock made by Chicago Locks. They can be picked, although I haven't been able to do so using hand tools - The lock has two sidebars and uses 8 single pins, not the pairs of pins seen in many other pin tumbler locks. The pins have deep grooves cut into the sides that the sidebar slots into. To deter picking the pins have very strong springs and shallower, 'false notches' cut into the side of the pins to confuse picking.
HTH.
