Launch Campaign sends it. You are asked to confirm, and the confirmation says the important part plainly: once it is sent it cannot be stopped.

The last check

• The recipient count — the number of real people about to receive this.
• The list name — the right audience, not one with a similar name.
• The email — the final version, not last week's draft.
• You have read the test.

Cancelling

Cancel Campaign stops a campaign that has not gone out yet — a scheduled one whose time has not come. Where a campaign was pushed to your tribes, you can cancel the tribe campaigns with it.

Deleting

A campaign cannot be deleted while it is being pushed to tribes, or after it has run. That is on purpose: deleting a sent campaign would delete the record of what your customers received, and the results with it.