In short, this feature does two things:
(1) It shows you how often a specific feature is found being used in the Google search results.
(2) It lets you see search results that should show those features on the live Google search results page.
The first case is the percentage number shown in the chart shows how often the feature is shown in the search results. So for example, “AdWords (Top)” in the graph above shows that 77.9% of the queries tracked by MozCast displayed ads at the top the last time it checked them. Of course, this is based on the queries Moz is feeding Google and this is taking out all the personalized elements.
The second is more interesting where you can replicate the interfaces, in many cases, by filtering the features you want to see on Google and then clicking on example queries listed.
Here I am asking to see AdWords at the top and the Knowledge Graph on the same search results page. MozCast then shows me sample queries that should trigger this behavior in Google. I can then click on a query and see the features live in Google:
There are some other neat features in this tool, so read about it on the Moz blog.