A border is a decorative element surrounding a column a column. It can also be used to visually separate two columns that have the same background color.
To apply a border, click on the row containing the column you want it applied to. In the properties menu to the right of the page, there are two sections:
Go to the Column Properties section:
At the bottom of the properties, you will find the Border attributes. Here, you can edit the border type (solid, dotted, dashed), width and color.
The end result could look something like this:
You can edit the border settings for each column in a row independently.
If you click on More options, you can also edit all 4 sides of a column's border separately. This lets you select different colors, widths or styles for each side of the column.