I was trying to understand how the reputation works and I don't quite get it. It is not the first time, that I see users who ask their first question, don't have other activities (like answering questions) and having 100+ reputation. Is transferred from other websites like stackoverflow?
Reputation isn't shared between sites, but once you've earned 200 reputation on one SE site, you automatically receive an "association bonus" of 100 reputation on any SE site.
This includes sites you are already a part of (including the site where you earned the 200 reputation), and sites you join later.