Do you need to download steam to install a game off steam

Well... Your question is not clear to me.

If you bought retail games, you don't need it, but if you want you can download steam app and register your game on steam app.

I bought COD 4 retail which means that I bought CD at gameshop in downtown.
After installed my game without steam app. but I registered my COD 4 on steam app so I can install my COD 4 without CD.