If you begin to experiment with the Mission Editor, be careful that you do not Upload any mission that you have not completed and fully tested. That sends the mission to the Custom Missions Managers for examination for possible inclusion in the download list.
The CMMs get many junk “missions†uploaded through carelessness or the erroneous idea that Uploading is necessary in order for the creator to run his mission.
I suggest that you first read all of the bold blue topics on the Missions board and study the Mission Editor Notes.