Basically all of the "fixes" are lib files: modifications to the game. Usually they are incompatible with each other so only one can be installed at a time. They are installed by moving the .lib file(s) into the Fighters Anthology directory. Some have other files that need to be installed as well, so always read the readme files. Some libs are small and change a few things, and alot of them are large and change every aircraft, weapon, vehicle, ship, etc. along with graphics, sounds, sometimes new aircraft panels, etc.
Missions hosted at the FA Resource Center are either groups of files, where each file is a single mission, or lib files which contain missions. Installation is just by moving the mission (*.M) and briefing (*.MT) files into the FA directory. Or if it is a lib file, moving the *.Lib file into the FA directory. Then, in FA you can fly the missions in the Single Mission menu. Or, some mission addons will replace a campaign, or add a new campaign, and these are flyable from the new campaign menu.
Basically I can recommend downloading what looks interesting and trying different libs and missions out. Centurian has a
huge collection of new WW3 missions, follow the link and click campaigns:
http://www.theforsakenoutlaw.com/FA/downloads.htm"520 missions of insanity and chaos in many, many, many campaigns ranging from Afghanistan to Iran to Cuba to Russia to North Korea to the Middle East and to South America."
Zephyr