Many of these maps are interactive. If you click on a place, you might zoom in and get more detail. Then again, you might not. Try it.
Similarly, if you click on the legend to a map, you might get a more detailed explanation of the topic.
Clicking on the arrows...
... will take you page by page through a specific subject, such as American History or Warfare.
Clicking on the Contemporary Context button bar...
... will zoom out to show what's happening in the world at this time in a specific field of human activity. The icons symbolize Cities, Government, War, International Relations, Living Conditions and Economics, respectively.
Although this atlas is non-linear in overall design, its backbone is probably the series of maps illustrating national political systems, so this is probably the best place to start if you have no particular topic you're curious about.
If you are curious about a particular topic, I don't have a search engine here, but you might want to use [CONTROL]-[F], and then type in (a) simple keyword(s), like soviet or world war.