You can add single contacts manually to the campaign, or associate a List of contacts to receive the emails.
Contacts added to campaigns will always start at the first event step of a campaign - even if that campaign has contacts in a different event step. If you associate a
Smart List, contacts who the system adds to that Smart List will automatically be pulled into that campaign. An associated
Recipient List will have contacts added to that Recipient list also automatically added to that campaign. To associate a List, select it from the drop-down menu.

To add a single contact, scroll down under Contacts and select either Add From List, Not Added, or All. (Not Added and All are tabs located on the right of Contacts). Select Add next to the name of the contact.

To remove a single contact, go to the Added tab and select Remove next to the contact you'd like to add. (Note: Contacts that are in a List associated with the campaign will be re-added to that campaign. You need to remove that contact from both the campaign and the List.)