As the name implies, CK2+ exists to give you more—more content, more choices, more fun. The goal is to offer a deeper and more challenging CK2 experience without straying too far from the original game mechanics or adding overly deterministic events. The purpose of this mod is not historical accuracy (although we try to preserve it whenever it’s not detrimental to gameplay), but rather to enrich the medieval sandbox that CK2 offers.
1) First find your installation directory. This will depend on your OS, and may not be (especially in the case of Windows) the directory where you actually installed CK2 itself: Windows: ~\My Documents\Paradox Interactive\Crusader Kings II\mod\ Linux: ~/.paradoxinteractive/Crusader Kings II/mod/ Mac: ~/Documents/Paradox Interactive/Crusader Kings II/mod/ 2) If the "mod" subdirectory doesn't exist in the above location, create it.
3) If you already have a "mod" sub-directory there, excellent. Make sure you delete anything related to CK2Plus prior to the manual installation -- this includes any old versions of the mod, anything that was installed by Steam Workshop (which we no longer use), etc. You want a clean slate when installing, even if you're just updating to a new mod version.
4) Make sure you've downloaded the latest .zip from the releases page
5) To extract the files from within, you'll first need a program like WinRar or 7-Zip. Once you have that, you should be able to just click to open the .zip file and you can move the files over to the "mod" sub-directory. Alternatively, you can use the extractor program to select the .zip file and select where you want the files extracted (the installation directory in #1).
6) Start the CK2 launcher. Check the "CK2Plus" box in the list of mods, along with "CK2Plus Expanded", if you so choose, then launch the game. When the title screen comes up make sure the checksum (the four-letter code to the left of the title screen buttons) matches the one listed for the CK2Plus release you just downloaded. If so, you're good to go. If not, you've either made some other alterations to the mod, enabled some other mods from the launcher, or made a mistake.