What is an XLAM file?
XLAM is an Macro-Enabled Add-In file that is used to add new functions to spreadsheets. An Add-In is a supplemental program that runs additional code and provides additional functionality for spreadsheets. XLAM files are stored with the .xlam extension. XLAM files are XML-based files similar to XLSM and XLSX file formats and are saved with ZIP compression to reduce the overall file size.
Example
Public Function Add(num1 As Double, num2 As Double)
Add = num1 + num2
End Function
After this, save the file with the .xlam extension.