Your pages are automatically set up with columns when you add them. Typically, your page will have two columns that both span 50% of the width of the page although this may not always be the case. You can change these column widths by following these instructions. 

1. Go to the page you want to update. 
2. Click on Page Properties. 
3. Click on Layout. 
4. Choose an option from the "Present column width options" menu. Please note that if the widths you want are not listed, you can type them in the boxes below this menu next to Column 1, Column 2, and Column 3. 
5. Click on Save.