about the callback function

[sandodo]

I am doing some source code on windows hook. The functions
JournalPlaybackFunc(), CallNextHookEx() and etc, I know,
are to build the loop to, for example, play back what recorded.
But the CALLBACks before the functions upset me, I am not clear
about what the functions are called through underground.
Does anybody can provide some information or drop
some web addresses on CALLBACK as referral?
Many thanks!

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