Some important information about modules in vb.net, those are given below:
1. Modules can never be instantiated.
2. Modules do not support Inheritance.
3. Modules can be declares as Public.
4. Module can be declared only in namespaces.
5. Members of modules are implicitly shared.
6. Modules cannot be nested in other types.
7. WE can have multiple modules in our application.
8. WE can call methods of module without needing to create an instance.
9. Modules cannot implement Interfaces.
10. We can say module is basically a class that has all the members as implicitly shared.
You can go to this link for knowing difference between class and module:
http://msdn.microsoft.com/en-us/library/7825002w(en-US,VS.80).aspx