@kek184 Your 'Home' column is what you've posted or responded to other's posts. 'Notifications' are the responds of others to your post. The 'Federated timeline' is the open current feed post. My pc shows the world icon for opening the Federated timeline. Hope this helps.
@KarMarJo57 Not sure what I did but I lost my "home" column. I only have Response Column, Notifications Col. and Timeline Col. now. Have gone thru all the icons, and settings, but don't find how to add more columns. Any hints? Thanks.
@kek184 try refreshing the page or start over and re-entry and see if it's still missing.