To specify your column width, click on the Columns Width button in the Table area. A drop down menu will offer three choices, including:

Fixed: This will keep each row the width it currently has, and allows you to customize the table column width to your liking using the mouse.

Percentage: This option will keep each row as an equal percentage of the width of the table

Fit to Content: This option will automatically change the table columns width based on the size of the text and/or shapes within the table cells

To manually change the width of a column, hover the mouse cursor over any table border line, and a line with a small arrow on either side will appear. Click and hold, and drag the border line to your desired sizing