The option Simple Combination supplies simple combination methodes with which you can calculate any other values. For example a surface can be determined out of the multiplication of the two options width and height. Furthermore you can use the Simple Combination for selected additions and string concatenations.
Presentation in the frontend
The Simple Combination is primarily designed for calculations in the backend, but of course you can have the result displayed in the frontend.
Settings in the backend
In the field "combined values" you select the options you want to combine (here width and heigth).
Next you choose the "operator value", here you can select between addition (+), multiplication (*), string concatenation or expression.