From Exterminatus Manual
There are two versions of the Exterminatus installer:
- Self extracting windows installer
- ZIP archive
The windows installer is recommended for most users. If you have trouble with the windows installer, try extracting the ZIP file to your Steam\steamapps\SourceMods folder, maintaining the folder structure from the ZIP file. Zip file users will also have to apply the patches from the Downloads page to get up to date.
See the Downloads page for a list of places you can get the installer from.
Exterminatus installs to your steam/steamapps/sourcemods/ folder, where it will create it's own ex folder. Everything Exterminatus creates or uses is kept in this sourcemods/ex/ folder.
Patches are small updates to the mod to update a subset of the files without requiring a full downlaod of whole mod. Patches are distributed as ZIP files ("compressed folders" in Windows speak). Extracting the ZIP file to your Steam\steamapps\SourceMods folder, maintaining the folder structure from the ZIP file should update just the changed files.
Installing Chapter Packs
Chapter packs are available from the Downloads page to replace the Ultramarines in the default EX install with another chapter. You can only have one chapter pack installed at a time as they overwrite some of the default files. Chapter packs are distributed as ZIP files and should be installed in the same was as Patches are (see above).
Don't forget to set up your name and controls before joining your first game of Exterminatus. Nothing says n00b like being called "Servitor". Binding controls for secondary fire is fairly important in EX, but there are no special keys you need to play.
If you change your screen resolution, it is best if you exit the game and re-load it before playing to avoid a crash (and loosing your settings changes).
Finding A Game
For reasons unknown EX servers rarely show up the the steam server browser list, but THEY ARE OUT THERE. Check out the Servers page for a lit of EX servers and instructions on how to connect. If nobody is home then take a look at the Exterminatus Steam Community page for scheduled games.