How to add comments to custom functions in excel just like the comments of Excel built-in functions?

addon_yuan 

I'm not sure you can do it "just like the comments of Excel built-in functions" BUT if you're using LAMBDA to name your custom functions, there is a way to add comments at one of the stages of development, and that can be used to explain how to use the function. The hyperlink in the preceding use of the word LAMBDA takes you to a resource that explains it. This image is from that page, where you can see the "comment" box