In Excel on the Analytic Solver tab on the Ribbon, click the Help dropdown menu and choose Examples. This opens a workbook. Select "Optimization Examples and another new workbook will open which contains the examples used for conventional optimization in the User Guide.
The Link/Worksheet "Inventory Planning" is the one you're interested in. We recommend running this example with Guided Mode on (Help - Operating Mode - Guided Mode), since it will give you a better explanation of what happens, as the Platform first finds the IF functions, then attempts to transform them into equivalent sets of integer and continuous variables and linear constraints, and succeeds and solves the model to optimality.
To read about the transformations that the Platform is making in EXAMPLE5, click Help - User Guides - User Guide and go to the User Guide's last chapter, "Building Large-Scale Models". In the section "Improving the Formulation of Your Model", read the subsection "Techniques Using Linear Functions and Binary Integer Variables", especially the part about IF functions.