1. The Console is that nifty thing used by *nix admins and some windows ones as well. It looks similar to DOS, but it's not a DOS. You can start it by running cmd.exe (Start Menu -> Run -> type cmd.exe and enter)
2. First - find where Lineage 2 is installed. It's something under c:\program files, assuming you didn't change default options during installation. In this guide, I'll refer to this folder as LIN2DIR. It's probably c:\program files\Lineage 2 or c:\program files\Lineage II
3. Download l2encdec package from the site. Unpack it - you will find a folder with a few files. Copy l2encdec.exe and patcher.exe to LIN2DIR\System. If you're planning to use loader, copy loader.exe and gg-bps.dll as well (important only for certain old L2C2 builds)
4. Make sure, that Lineage 2 is in "fresh" state. The easiest way to do so, is to start it normally and do "full check". If you know how to do it w/o "full check", you don't need this guide anyway :). Also, be sure to remove folder named backup under LIN2DIR\System - this is a folder created by patcher.exe. If you ran patcher.exe at some earlier time, please make sure backup is not there (deleted, moved), before proceeding further.
5. When everything is ready, you have two options:
   1. Using explorer, go to LIN2DIR\System, and start patcher.exe . Console window will open, and some shit will happen. When the process is completed, there will be "press any key" at the bottom. If something goes wrong there will be "There have been problems" line. It means that you have either: a) backup directory or b) game with already reencrypted (or just damaged) files. In such case, go to point 4 and repeat the process.
   2. Start console as explained in point 1. Enter: cd "LIN2DIR". Quotes are important - so don't miss them. Now enter:
      
      cd system
      patcher.exe
      
      The same will happen, as described in 5-a. If you get errors, you can go to point 4 and repeat everything, or
      
      rd /s /q backup <-- This will remove backup dir if you forgot to do it earlier. Be sure that you're under LIN2DIR\System before you press enter :)
      patcher.exe
      
      If you still get errors, go to point 4.
      
      IMPORTANT: There may be one more reason for errors - encrypted l2.exe file. In such case, you're probably using build of Lineage 2, from +/- middle of C2 to C3 (important for people using private servers). If at the end of patcher's output you can see a failed attempt to modify l2.exe, it means that this is the case. You will have to use loader.exe to start Lineage 2 (opposed to what is written in point 6)).
6. Now you have Lineage 2 in "patched" state. Backup dir created by patcher.exe holds backup of all the files altered by patcher.exe (never hurts to have a backup). You can run Lineage 2 normally as always (do so and see if it works). IMPORTANT: if there's any update issued by NC soft, you will have to do "full check" and repeat everything from point 4. There're other options, but you shouldn't be reading this guide, if you know them :)
7. Almost every patch present on the site is installed by overwriting files. Sometimes trival and obvious file renaming is required :) The only exception are patches with xdelta files. XDetla is a binary patcher. Simple to use. Get it, type xdelta --help, learn how to use it. At the time of writing this, the only patch that requires it, is C3's l2font.utx modification (colored map + naked de loading screen).