How to create custom Excel functions using Visual Basic for Applications (VBA)?

To create a custom Excel function using Visual Basic for Applications (VBA), follow these steps:

Open Excel and press Alt + F11 to open the VBA editor.
In the VBA editor, insert a new module by clicking on "Insert" from the menu bar and selecting "Module".
In the module window, write the code for your custom function. For example, let's create a function called MultiplyValues that multiplies two numbers:

Function MultiplyValues(num1 As Double, num2 As Double) As Double
    MultiplyValues = num1 * num2
End Function

Save the workbook by pressing Ctrl + S or by clicking on the save button in the toolbar.

Now, you can use your custom function like any other built-in Excel function. In any cell, simply type =MultiplyValues(A1, B1) to multiply the values in cells A1 and B1.

Note: When saving an Excel workbook that contains VBA code, make sure to choose the file type "Excel Macro-Enabled Workbook (*.xlsm)" to preserve the VBA code.