You can choose who receives a campaign you send yourself. You can't choose who receives an automated one, because those are triggered by what a guest does.
Campaigns you send yourself
If you have more than one location, you can send to a single location's guest list. That's the only way to narrow the audience at the moment.
Pick the location from the dropdown in the builder. This works for texts too. The location picker only appears if you have more than one location.
Automated campaigns
Lifecycle campaigns, like cart abandonment, go to guests automatically based on what they did.
Event campaigns, like Valentine's Day, go to your whole guest list.