Some user in the main page has 101 points without any questions or answers, because of an association bonus. Could someone please explain what is that?
If you are already a member of a Stack Exchange site, when you join another site, you get an association bonus of 100 reputation on the new site.
From this page:
You gain reputation when you associate accounts of two or more Stack Exchange network sites, and at least one of those accounts already has 200 or more reputation: +100 on each site (awarded a maximum of one time per site)