Hi, Moxy and welcome to AAA.
The first thing for you, is that in the process of making a mission, you must remember to
make a file of the name that you choose
before you save the mission, preferably first so you don't forget. The file that you make and name will be in the exact location in the appropriate mission folder. For example, you can make a mission using the Full Mission Builder editor ( FMB for short ) which can become a single mission. Make a file with a name that you like in the Single Missions folder under the country that you want, Great Britain - Uk, for example. With single missions, you must remember the all.ini file. You'll learn how to do that. So, I am recommending that you start by making single missions before you graduate to campaigns and careers.
Second, in the mission building you must remember to check the box in the editor when the plane is loaded which you want to fly in the mission. CHECK THE BOX " Player ". You must do this to make the mission run.
Single missions, quick missions, campaigns and careers are Veeeeery fun, especially if you share them with people online and offline-such as your friends-they could get hooked.
One of my goals is to make a comprehensive FMB topic someday.
Feel free to ask questions. Have fun!