Often, when we need to derive data, we may need to incorporate some built-in functions in Tableau. Functions are reusable, "callable" code that can be used in calculations. Functions also return some kind of value.

In the calculated field editor, there is a faint arrow on the right side of the rectangle. When you click on this, it will expand and show a Help box for functions that are supported in Tableau:

When you click on the dropdown of the help window, you will see a list of the function categories available: