Welcome to the Diesel Academy.
There are many levels. Each level will walk you through a certain aspect.
If the concepts markup, DSL and wikis are not familiar to you, read about Markup and DSL first.
You can read the Big Dieselapps Overview and/or go through the detailed sections below:
More subjects and articles worth reading:
Message reliability: https://www.infoq.com/articles/no-reliable-messaging - good article.