What language do you want to make the call from a global function?
If you mean VB6, you will need to reference your new COM object in your VB6 project, and create an instance of the COM object like this:
Dim objA as New YourATLComObjectName
If you mean C++, you will need to call ::CoCreateInstance with the GUID for your object.
The two things you will need in place to make sure your VB project can see the object:
1) The DLL needs to be registered which happens by default when VS compiles it. When you install it on a users machine you use regsvr32.
2) The DLL needs to be referenced as one of the resources that you bring into your project.