How to use tags to create Campaigns lists and email clients?

How to use tags to create Campaigns lists and email clients?

Hi,
How can I use tags (from Contacts) to dynamically create marketing lists and email my clients regularly?
I really hope that the option is not to create a manual list every time because this is just not manageable. 

I know how to create segments but I can't find how to use them in any Campaigns workflows.

Please let me know.
Thank you