First of all, what's your PC specs. Crysis needs a good system to run the game properly.
Take your Crysis DVD and put it in your CD/DVD-ROM.
Next, if autoplay is enabled, then a dialog box should appear asking you to whether install, uninstall, play etc..
Choose install and enter your CD key that should be on the top right corner of the box. Install the game in the default directory. Update or patch the game. Then run it.
OR, if you've got the pirated one that needs to be cracked, then we won't help you.