I was going to write about this myself, but it turned out to be more bigger and more complicated than I thought. So, with the words of two great philosophers in mind
I gave it up because I wasn’t immediately successful
That’s all right, boy, anything that’s hard isn’t worth doing
I did a net search and found this website.
It doesn’t answer all my questions, like what does it means if the either of the perfect tenses are used with a hace-time construct, but it’s otherwise pretty good.