The Add Contact to Campaign action is only available when a CRM database is associated with a Classic Program.
The Add Contact to Campaign action allows specific contacts to be added to an existing Salesforce.com campaign. You must enter a valid Salesforce.com campaign ID. If you also want to specify the Campaign member status, type in the exact member status text as defined on the Salesforce.com campaign. Without entering a campaign member status, the default member status as defined on your Salesforce.com campaign will be used. All contacts that match the Add Conditions are synced to the CRM system and added to the campaign. You can specify a member status value here as well.