Most of us work in MS Word to create invoices letters etc. Formulas always start with an equal sign. In order to use this first of all you would have to add it to the Quick Access Toolbar.
You can also check out the online documentation from Microsoft that explains each function in detail.
These cell addresses can be linked together with standard mathematical operators. There is a list of formulae you can choose from the many based on the requirement. Go to the Quick Access Toolbar that is located on the title bar and from the drop down box select More Commands. Modern versions of Word include almost all the symbols and structures a math professor could need.