Macros usable to other users
When you create a macro and send the workbook to other users, unless they have their settings such that they can run a macro, you need to give them special instructions so that the macro runs.
Surely, there must be a way to send a workbook with a macro in it to someone without having to tell them to change their security settings which often causes them to think they're doing something to put them at risk.
Kenneth Barber commented
You just have to tell them to change their setting to "Disable all macros with notification". That way, they know that a macro is in the file, but it doesn't run without their permission.
You can - add a certificate to your code and get your users to install it. Only needs to be done once and if they tick "trust everything from this publisher" the security warning will not appear since they have your certificate installed.