Somewhere I downloaded a sample and it has a folder called custom functions.  Inside it are fields with extension of fmfn but when I try to open them, this new Mac can not identify them.  Can someone explain how I can use them and how to create them?

There are a couple of places you could have downloaded them from. However they are NOT going to open them by clicking on them, they have to create the Function in one of your files Main Menu  (File >> Manage >> Custom Functions...) New and then transfer the Function to the Edit Box.

My guess would be you downloaded them from GitHub. They aren't really usable in FileMaker. Try opening them in a text editor...or on GitHub. It will show you the text which is content of the custom function most likely.

Thank you guys.  I had never seen that before.   I do not know why they were included at all so I thought they must be useful or important.  I'll give it up then.  Thank you.

 I thought they must be useful or important. 

Actually,  they are both. Read the descriptions of what they do and if you have a situation that fits the description you can save yourself a lot of of coding.

 

Read that help regarding custom functions here

Thanks Lee.  I know custom functions are great I just meant that I thought that folder and those files must have been important or useful to be included.  I have been using custom functions already and they really are handy.