Assigning Categories
Q. How can I get a list of all the contacts which have an e-mail address and assign a category to them?
A. There are a couple of ways to do this. If you want to assign the category to contacts that have an entry in a specific e-mail type you would run the Edit, Find against all records using the e-mail type (i.e. Email: Home from the fields dropdown) with the "Is not empty" condition. That will return all records which contain a value in that specific e-mail type. Then you would use the Edit, Assign, Categories option with Current List option from the Apply To: dropdown and Assign from the Action: dropdown.
If you want to assign the category to all contacts which have a value in any of the e-mail types (i.e. Email: Home or Email: Work) you would perform the same steps as above but use the "All Email Fields" choice from the fields dropdown instead of the specific e-mail type.