You can add columns and rows to a table in ScreenSteps using the web editor or the desktop editor. If you are not familiar with how to add a table content block to your article refer to the Add new content to an article article.
Adding columns and rows
1. Click on table to enter edit mode
2. Select a cell > click on row/column options
After you select a cell (1), you will see options to edit the cell, or add rows and columns to the table. Circled below (2) are the options to add rows or columns.