We do not not have a tag feature (at the time of this response) where you can add tags to contacts and then run searches on tags. But we do have functionality to provide what you are wanting to do and that is with our "Lists" feature. Instead of adding a tag to a contact, you would add a contact to a list. Whatever tag you are wanting to create, say Medical Device Manufacturers for example, you would create a list for.
And then when you have contacts that fit that category, you would add them to that list. You will be able to view, work, and email each of your lists which should be your different groups and categories of contacts and accounts.
Here is a video that explains Lists a little more: