This app is designed to help web services that are planning to blackout their services on January 18 to protest against SOPA and PIPA.
Instead of making changes to your website, you can just enable this app in your CloudFlare dashboard. And the service would do the needful automatically.
Stop Censorship would randomly blacken content on your webpages and users would be shown details on why that is happening.
The idea is to save you the trouble of making changes to your website manually. And keep the service active while still registering your protest against these new acts being discussed in USA.
CloudFlare spoke about the initiative:
We wanted to provide a way for people who wanted to raise awareness about SOPA and PIPA to do so effectively and without hurting themselves in the process.