Let's say that you are adding a Group of 100 people to receive a Broadcast.
There's 1 person in that Group who cannot receive the Broadcast. In that case, you'll want to exclude that person when you're composing the Broadcast
Here's how you do it:
Toggle the 'Exclude Contacts' to on when you're composing the Broadcast.
Then, search for the Contact or the Group that you'd like to exclude.
If you don't have a Contact or Group you need to exclude, you can create one.