The installation is very easy, just follow these instructions:

  1. Unzip the WinRAR archive to the location where you want the game installed
  2. Move the "GameData" folder into your game folder
  3. Move ckan.exe to your game folder
  4. Run ckan.exe
  5. Once CKAN is opened, select "Settings" and then "Compatible KSP versions"
  6. Tick the "1.2" and "1.3" boxes
  7. Click on "File", "Install from .ckan" and open "Roboweb KSP Mods.ckan"
  8. Click "Continue" and wait for everything to install
  9. All done!
If CKAN gives errors whilst downloading or installing mods, just repeat step 7 and 8 until it works.
CKAN saves the files locally so it will just resume where it left off, instead of starting all over.
Yes, really, just keep trying until it works. This has to do with the amount of data you are downloading at once.