The Formula Designer window is split into three main areas:
Click here to see the screenshot

Formula Designer displays a toolbar, which allows you to access the functionality also accessible from the Formula Designer menu bar. Once Formula Designer is open, the Formula Variable Pane is populated with variables which are displayed in a tree-like structure.
Formula Variable Pane
The Formula Variable Pane is populated with the available variables. The different types of variables are:

The variables within each group are displayed in alphabetical order.
Tip: By default the Formula Variable Pane is docked to the left of the Formula Designer window. To make this a floating pane, drag the title bar of the Formula Variable pane to another part of the Formula Designer window. In addition, double-clicking the title bar of a docked pane automatically moves the pane to its previous floating position.
Formula Edit Area
As you compose your formulae, the Formula Edit Area displays your formula in a hierarchic structure. You can expand or contract parts of your formula so that you can concentrate on isolated areas.
Right-Click Menu
Within the Formula Edit Area, right-click the mouse to display the context-menu:

The top section lists the operators available to use in your formulae. See Changing Operators for more details. The middle section of the menu allows you to select and deselect percentages for numeric values. You are also able to assign negative values to your formulae. The bottom section allows you to Edit Numeric Operands, delete elements and remove brackets from your formulae. Formula Display Area

This pane displays your formula in its traditional algebraic form only. Whilst editing, the Formula Display Area allows you to see your formula in its entirety.
Note: You can edit formulae in the Formula Edit Area only.