While I was working on my first viz (a map), I happened across a place where I could add in Census to my map.  It drove me crazy when a week or so later I couldn't find it again, but at last, I figured it out.  

 

Go to Maps (in top menu) and select Map Layers from within the Maps menu.  This will pull up the Map Layers pane on the left side of the worksheet.  Go to the pull down menu under Data Layers to see the various types of Census data available.

 

I have yet to delve into this cool little tool, but at least I'll be able to find it again when I'm ready.