All of your campaigns, whether draft, active, or completed, are available under the "My Campaigns" navigation menu on the lefthand side of your screen.
Then, once your campaigns dashboard has opened, you can view all of your previously-created campaigns. You can also click the three dots on the far right of each campaign to view the campaign snapshot (details of the campaign), resume editing, duplicate the campaign, or preview the campaign.
To launch any campaign currently saved as a draft, simply click "Edit Campaign," then complete the campaign set-up through "Launch Campaign" in the last step.