With that knowledge, we will work into what handles are, right now, specificially, I'll give you some info on the trigger handle.
In GUI, traditionally, triggers have events, conditions, and actions. The events cause it the actions to execute only if the conditions are met. Again, the event causes the trigger to react. If the conditions return true, then the actions contained in the trigger will be executed.
The trigger handle itself is the exact same thing, and events, conditions, and actions are all defined within that first '_InitTrig' function.
NOTE - The name of the '_InitTrig' function may be changed, but the function's name MUST ALWAYS be the name of the trigger in the trigger editor (the name that highlights blue when you select it, next to the white page-type picture) with '_InitTrig' attached to it. To make things easy, when you change the name of the text that you select (which highlights blue), it also changes the name of the '_InitTrig' function.