Well, maybe i am stupid, but i just don't get it how statistic works. And i am curious about it, maybe someone could explain?

What are signups and unique authors? Whats the difference?
Whats the difference between submissions and entries?
Why entries - 1576, submissions - 1560, unpublished - 1520 and unfinished - 16 (1536 in total)? What does that mean? Why numbers are all different?

Thanks ^_^