If you are making a method that can be used in another .net app, you have no need to use export of any kind. You just have to make sure the place where your code is, is public and the function you wish to call is also public then just call it, .net intellisense will show all available methods.
It also sounds like you do not have Option Explicit/Option Strict turned on, this is a must, have a quick search to see how it works if you have not come across this before.
btw. You can add more then 1 project into a solution and make one dependant on the other which makes managing code much easier
Public Module modFileAccess
Public Function GetTempFileName() As String
Return IO.Path.Combine(IO.Path.GetTempPath, IO.Path.GetTempFileName)
'In the other project