This page in a nutshell: Contentious topics are specially-designated topics that have attracted more persistent disruptive editing than the rest of the project. This system replaced the former discretionary sanctions system, and there are several differences between the two.
The guide is used to describe the differences between the former discretionary sanctions procedure and the new contentious topics system. For a detailed version or if you are not familiar with discretionary sanctions, it is instead recommended to read the contentious topics procedure page.
Wikipedia:Contentious topics/Comparison with discretionary sanctions
