Thank you for your question and your screenshot. From the looks of your screenshot, you have tiles enabled for your page. Tiles and widgets are not intended to be used interchangeably yet as one or the other as described in this document. Widget and Tile Comparison Grid for Cloud (2016.3). We have worked to move towards the use of tiles over widgets as they are more robust to use moving forward. To add a new tile, select 'add a tile' from your page and select a new tile from the given menu.
If you are intending to revert back to a widget page or use widgets, you can select the 'overview page' page option in the advanced menu of your space/group settings. If there is no 'advanced' option available when selecting a space/group settings, file a request to the Jive Support team for more information on this issue.
And in case we missed your question... if you are attempting to make a two-column page into a three-column page you can do that by selecting Edit page > About. You can select a different column layout from there which will allow you to add tiles to the right side. Here's a screen capture of what it looks like: