I am following this tutorial series on youtube and I am doing ok until I get to this point.
Once I click on the actor class I end up with a grid with this orb in the middle rather than a blank slate:
What is this and how can I make it go away?
The Orb is the actors default root component (see component list to the left), if you add any other component, it will replace the orb. I dont even think the orb is visible ingame, it is just a default root component since the actor needs one. The video is from an earlier engine version before the orb was used to indicate the root component I think. Perhaps blueprints dident need an initial root component in that version, or perhaps it was just not visible.
Hope its any help. 
This got me there. Adding a new component didn’t remove the orb, it just made the new component a child of the root. Dragging the component onto the default root makes that component the new root.
Thank You!