Hiya, Old Crow.
Understand what your asking. Afraid, at first...it will be a little messy. Ha!
Whether for a single mission, or a campaign (set of missions), all the basics will work.
But, for either, you will need to see how the groups of various files work together. What I mean, say for a campaign, is the basic campaign file will list a set of missions. For each of those missions, there will be a list of spawning files, etc., etc.
You need to understand the file structure to know what, and where, to change the entries, to make it all work. Just chose a campaign, and pick through it, to learn about the various files.
Of course you need to remember that...IF there are ANY mistakes in any of those files, the mission/campaign will not load. Mistakes such as typos, or calling for a/c or objects you don't have.
As far as your spawning files, it's best if you have MB up, and working.
I'll suggest looking at a few of your existing spawn files, and try to pick ones LIKE the spawn you want. Then...copy 'em, and rename each copy.
The copied/renamed spawns are the ones you'll tinker with.
Then, start up MB, creating a 'dummy' mission, just to use as a building block. With that dummy mission loaded in MB, now you have access to the editing end of spawn files. Simply edit those 'copied' spawn files as you wish. It's easier to use copys of working spawns, instead of trying to create new ones, and change them as you wish.
Of course, it's also possible just to hand edit spawn files, but be sure to use workable copys!
Hope this helps.
