Here is an overview of a campaign life-cycle:
Step 1: New
A new campaign can be created by scratch or imported from the Campaign Library. No one will receive your communications until it's launch.
Step 2: Launched
Once a campaign is launched the last version you were worked on is available to the universe.
Step 3: Editing
Found a typo or need to make a change? Just edit the campaign. Don't worry, no one will see your changes while you are drafting and modifying the campaign.
Step 4: Relaunch
Happy with your changes? Relaunch the campaign to publish to the universe.
Repeat steps 3 and 4 as often as you like.