Not the easiest question to answer. Campaigns come in all shapes & sizes & (like all 3rd party files) will not all be configured in the same way.

Installing a campaign itself is simple. Paste all .mis & .cmg files into the CFS1\Campaigns folder. This will work if it uses only default aircraft & scenery.

Many campaigns use 3rd party aircraft which must be correctly installed for the missions to work. These aircraft are not always included with the download so you should read the instructions carefully to find which ones are required & where to get them. Some aircraft might no longer be available as CFS1 is getting old now & many small sites have closed down for good. The most important thing with aircraft in missions is their folder names so you could possibly use a similar 3rd party aircraft by renaming its folder. The folder name must be exactly right for it to be recognised by the missions. Don't do this with the default aircraft.

The same goes for 3rd party scenery. This is not so important as the missions will still work without it installed. My best advice is to read the included instructions. If you have problems with a particular campaign post again with full details. I won't promise but it's possible I can help.