The Knowledge Graph is a huge body of data sourced from a variety of trusted sources on the internet:
The Knowledge Graph is built on a few key concepts. Google is seeking to understand the meaning behind words, not just the queries ("strings" of words) in themselves. It's also seeking to answer questions for users within the SERP, which is why you might get all sorts of different Knowledge Graph results in the SERP.
Some of the most well-recognized types are:
First, a caveat: while you can implement the right markup, Google doesn't have to respect it or include the marked-up data in the SERP. However, if you do implement the markup, you have a better chance at getting it included in the SERP.
There are three elements Google says you can influence if you're a webmaster for your site:
In order to customize these three elements, you simply need to implement the respective markup in the page source on any crawlable page on your site.
Once you've implemented the markup, go ahead and test it with Google's structured data testing tool.