Once you have those installed all you have to do is download the release and drop the map files into a folder.
Open Sauce (Allows for engine extensions).
Halo Custom Edition (A unshackled version of Halo PC).
Halo Combat Evolved PC (Needs to be a legit version with a CDKEY).
I recommend checking out the videos linked at the bottom. A full list of changes is way too big to make. It is finely tuned to provide an optimal experience on Legendary difficulty, just like the original game was, and also includes an all new difficulty level "Noble" difficulty. The mod not only includes new weapons, enemies, vehicles, areas to explore and levels, but also contains easter eggs such as terminals that explain the changes to the story, and skulls which add new twists onto the gameplay. SPV3 is a total overhaul of the Halo 1 campaign for the PC. This is only the launch of the first half, the second half does not have a launch date just yet The work these guys have put in over the countless years has been insane and while it's not exactly the definitive version of Halo CE due to lots of changes made by the development team it's much more than just a simple mod. Halo SPV3 is set to launch in around 8 hours.