If you are working on a Task Board, the Board Settings dialog’s Column tab can now let you hide or show columns.
To use this feature, open the Board Settings dialog by clicking on the gear button that appears on the top-right corner when you are viewing a Task Board, and then switching to the COLUMNS tab.
When you hover over any column in the list an options button (three dots) will appear:

Click on that and you will see the Actions menu.:

This makes it easier to manage boards with large numbers of columns.