Hi Jack48271,
Welcome to OPFEC!
All scenarios that ship with A2 (like "Trial By Fire", "Freedom Fighters", etc.) are compressed and cannot be loaded into the mission editor without uncompressing them first.
In order to uncompress them you need some 3rd party tool like
Eliteness.
Once you got the tools go to your Arma2 folder (on my box that's "C:\Program Files\Bohemia Interactive\ArmA 2"). Go to the "AddOns" folder. This is the folder where all the important game data lives. Since it's important game data you don't want to change it.
So copy all the PBO files that start with "mission" (here that's "missions.pbo" and "missions_ew.pbo") to your Desktop and uncompress them. Some new folders will show up (like "missions" and "missions_ew"). Open them and navigate to "ca\missions\Scenarios".
Voila! These are the missions you've been looking for.
All you got to do now is to copy them to your mission folder (e.g. "C:\Users\YourName\Documents\Arma 2\missions"), start Arma2, enter the editor and load them.
HTH.