There are two ways to add columns to your turnsheet:
Click on the arrow beside each Column Heading to open the Column Heading menu and select Add Column, or
Press the + button that is situated beside the last column in the turnsheet.
By default, the columns are placed at the end of your turnsheet, in order to move your column hover over the Column Heading until a hand appears and drag and drop it to your desired place. Additionally, you can move columns via the Reorder columns dialog in the turnsheet toolbar.