A Public Variable is just that Public.
This means from a Module Standpoint (not a form or report module which is actually a class module) you can reference the Public variable simply by using it in code.
For Public Variables in a Class Module need to have their reference point also identified (which means they have to be activated) in order to reach those variables. Example the Form "MyForm" needs to be open to see the Public variables declared in its Declaration section: Using Forms![MyForm].[Public Variable Name].
HTH