Robdcamp, there is not an actual mission editor in the Strike Fighters series like is found in LOMAC for example.
A good way to train in SF2 is to use the Single Mission option. There you can select what aircraft to fly, the year of the mission, the type of mission available for the aircraft selected, the time of day the mission starts, the weather and the intensity of enemy air activity and anti aircraft defenses. Also down in the options page you can manipulate a number of different difficulty settings including the realism of the flight model and the skill of the enemy AI.
I have found that by adjusting those you can often predict what level of opposition you are going to face in a mission. For example if you know when the Mig-17 and Mig-21 went into service with the North Vietnamese Air Force you can select a date that issuers you only encounter Mig-17's.
With that in mind I would recommended flying single missions that have all the settings in your favor to start with and then as that gets easy adjusting it to make them progressively harder. Another recommendation if you just want to through the aircraft around the sky with out worry is to change the start location from "near the target" to "in air" or "at the air field" in the options menu and then move the way points in the mission map screen well clear of the target area. I that way you should have clear sky to play with the aircraft without interference. Just remember to hit refly if you don't want to save the result of the mission on the profile you are using after you exit it.
Outside of that I would recommend that you go to CombatACE and look into the "SF2V Air & Ground War Exspanion Pack v2.0 Gold
" and its updates.
Finally there is in fact a mission editor for the Strike Fighters 1 series but none for SF2 yet. I do not know if there is a way to use it with SF2 given the difference in file structure of the two games but you could ask at the CombatACE forums. You can find it and a tutorial for it here SF/WO* Utilities/Editors