Drag and drop the Buff Element (Found under the Gameplay Tab) from the Elements Library in the fourth column of the Sheet Builder, into the 3rd column which is called the Sheet Editor.
The Field & Buff Element on Role can be clicked at any time to add that number to your Dice Roller total. Additionally, if your element is linked to a Dice Pool in Advanced Settings, when clicked, they will automatically add that Dice Pool to the Buff clicked.
To access advanced settings in a Field & Buff Element hover over the upper right-hand corner of a Field & Buff Element located in the Sheet Editor. Upon hovering your mouse over it, you should see a gear icon appear which will allow you to access the advanced Field & Buff Options which include: