If you need to quickly add a few contacts to your audience, here's how. Keep in mind you can also add lots of people at once using the import tool.
If you're adding someone who already exists in your audience, you'll be alerted so you can make your changes to the previous record.
It's OK for someone to be part of more than one group in your audience. If you send to three groups (at the same time) and Bill is in all three, we'll make sure he only gets one copy. Bill would want it that way.