The function DATE is very useful to create your custom dates. This article will explain you how the function works
The functions NOW & TODAY are very useful in Excel. It's the only way to build dynamic date to calculate gap between dates.
If you want to calculate the difference between 2 dates in Excel, you have to use a hidding function . It's the function DATEDIF.
This article is a glossary of all the Excel functions to return the first day or the last day of the Month, the Quarter or the Year