Add a help message to a custom added function

I've added a custom made function to a spreadsheet. The function works. When I use in-built functions, when I type in the names of the functions I get a grey backed message advising what the function does. I believe it would be called a help message (although I'm not certain that's what it's actual term is, hence the difficulty when looking for help on this).

Is there a way to add in a help message for my custom built function so when I type it in, it brings up this grey box telling me what the contents of the inputs should be? (Apologies if my description isn't clear).

Many thanks for any help

John

Hi Marcol

Many thanks for the pointer. I tried to follow what was written, I'm not sure this is exactly what I'm looking for (if I knew the correct terminology it'd be easier for me to communicate what I was talking about).

Hopefully the following picture is a better way of explaining it.

Help return on Excel vba.jpg

When I type in 'Month' as a function it produces the grey box saying 'Returns the month, a number...' etc. When I type in my function 'MonthlyPIPayment' I want to see a grey box advising what the inputted variables are. Any ideas?

Much thanks

John