How do I select a campaign for my workflow?

Workflows are not associated with a campaign. However, you may tag a campaign’s subscribers all with the same tag, and start a workflow with the condition Tag is, and choose the tag you applied to the campaign’s subscribers.

To do this properly you would need to follow this pattern of actions:

  1. Create your workflow.
  2. Create a tag name in the workflow.
  3. Complete your workflow and choose Save and publish so your workflow is ON.
  4. In Search Contacts, conduct a search for the proper campaign’s contacts and add the tag you created in the workflow to the contacts. The key takeaway is that the workflow must be ON (saved and published) before you apply the tag to your contacts.

If one of my contacts is located in more than one campaign, will that contact the same message within a workflow more than once?

Because marketing automation workflows do not operate based on campaigns, there is a chance that a contact included in a workflow, that is present in more than one campaign in your account, could receive more than one copy of the same message you included in the workflow.

To avoid this, create specific segments of contacts and do not start your workflows with overly broad conditions. A good example:
Instead of starting a workflow with any subscription method, choose a specific method, that is, a web form associated with a specific campaign. This way, the workflow shall only apply to those contacts who signed up via the specified sign-up method.