If you'd like to turn on Invites, Followups, or Second-Followups for your campaigns, you will first need to enable these features within the main Campaigns view.
On the left-most column of every campaign is a drop-down menu - there are several Options to enable.
I - Invites
F - Followups
S - Second Followups
Once selected, you will see which campaigns have which features enabled according to their symbols (IFS). If the drop-down button shows no text, it means no features are turned on for this campaign.
Once the correct features are enabled for each campaign, press the 'Enable' button to actually run campaigns.
You can sort your campaigns according to the features they have enabled by clicking the 'Up & Down Arrows'.