I would like to send an email to people who have both tag1 and tag2 (and not tag1 OR tag2). How do I do this?
It is not possible to set your recipients to more than one tag - instead what you will want to do is first create a filter for this group of folks, then add them to a list. You can then set your email recipients to this newly created list instead.
Complete and current information on how to use NationBuilder is available in the documentation section.