As with any problem, tackle it one bit at a time. Try posting the shortest subroutine that you find most indigestible and highlight the bits you don't understand.

Then use the knowledge you gain from the explanations given here, to add brief comments to similar constructs in the rest of the code.

Then isolate the next routine that still taxes you and post that.

This should get you up to speed on what is there very quickly and will allow you decide whether the comments are enough, or if you want to refactor to your tastes.

You may find that once you've learnt to recognise the constructs, that you are happy with them.