Faulty Challenge electric drill

I have a not overly used faulty Challenge mains electric drill (from Argos). It has failed due to a small broken plastic bit and two small contactors no longer being in their rightful positions in the on/off/speed control switch. Therefore not repairable by me and not of a value (if it were possible) to be worth repairing by anybody else. Everything else looks good but has been let down by the switch. Thus demonstrating (amongst other things) the environmental folly of cheap tools.
Just a couple of questions that struck me when examining it though. How does the (electric) reversing switch work (in simple terms please)? What device is used in the trigger to provide variable speed control?
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