Please allow me to help you understand this
1) Only public webmaps are supported for MapViewer at this point (although this might change in the near future) which means the webmap has to be public
2) The three columns basically act as a filter for choosing webmap and they should be read as below
- My Content - Webmaps created or added by you to your org account but must be shared publically
-My Org- Webmaps created or added by other users in your org but must be shared publically
- Public - This is self explanatory, which means created by others and shared publically outside your org.
I hope this helps.
Nakul