How do Apps use Multiple Processors?

I should like to understand, how applications use multiple processors on a server, if indeed they do fully.

Take an Office app like Excel for example, on a Terminal Server, with 4 processors. Will the Excel executable actually make use of the 4 processors with multiple bits of the job at hand being handed to the other processors?

Or will it simply use one processor that it is ‘assigned to’, and the only real advantage in this example, is that there are still three other processors for other programs/apps/users on this terminal server to make use of.

Trying to get a crystal clear understanding, so if anyone knows of a good white paper on the subject, feel free to quote a link. 🙂

Thanks,
Andrew