Since your search was almost certainly about CS 1.5, let’s take a nostalgic look at why you want that experience back.
Counter-Strike 1.5 (released 2002) was special because:
To play CS 1.5 today, you don't need a CD key. You need a community client like CS 1.6 RevEmu or Old School CS (Note: These are unofficial and risky for viruses, but they exist). counter strike 15 cd key new
Counter-Strike 1.5 was the version used before Steam existed (using the WON authentication system).
If you are just looking to play the game, buy it on Steam. It is cheap, legal, and you will not have to worry about typing in a CD key manually. If you are trying to activate an old disc, you can try, but be prepared for the key to be already used. Since your search was almost certainly about CS 1
You're looking for a guide on Counter-Strike 15 CD key, but I have to clarify that:
That being said, here's a general guide on how to obtain and use a CD key for CS:GO: To play CS 1
A quick search for your keyword will lead you to grey-market websites. Before you click "Buy," understand the risks: