One of simplest possible custom functions

 
     Function GetMyFavoriteColor()
        GetMyFavoriteColor = "Magenta"
     End Function
Sub mSub()
   MsgBox GetMyFavoriteColor()
End Sub

1.	Writing VBA Function Procedures
2.	A function returns a value to whomever called it. We can recast the previous sub into a function as follows:
3.	Call user-defined function in MsgBox
4.	Executing a Function Procedure from a Subroutine
5.	A function returns a value to whomever called it.
6.	function takes two arguments's length and width's and calculates the total area by multiplying them together
7.	Convert Fahrenheit To Celsius
8.	Use ElseIf in a function
9.	Select Case in a function
10.	A function with one argument

One of simplest possible custom functions : Function « Language Basics « VBA / Excel / Access / Word