The DAX language contains a number of functions relating to date and time, including a couple of functions that allow you to automatically create simple date tables. Many of the remaining date and time functions give you the ability to expand these automatically generated tables with additional columns of date-related information. If you've worked with date and time functions in Excel, then these are very similar, with the exception that DAX date and time functions work with the datetime data type.
Almost all the data models you'll work with will involve some form of calculation relating to date and time, and they'll usually contain at least one date table. In fact, if you are working with a data model in Power BI Desktop and you don't have your own date table, then, by default, it will automatically create a hidden...