Campaigns must be saved as drafts before you can add offers to them and submit them for review.
You can edit campaign drafts, but you can't edit campaigns once they have been submitted for review. If you need to edit a campaign that has been submitted for review, you must first send it back to drafts.
When you go to Campaigns > Draft, you can view any campaigns you've created and saved without submitting for review (approval). You can select a draft to edit (or even discard campaign drafts) from this page.
More information on how to use the Draft page can be found in these articles: