Call of duty united offensive expansion pack

I bought this game from a antique/ thriftstore and never got to playing it because for some reason there is only a disc two and it's pc. there is a code, I don't know if it's been used but I don't know what to do with it. if anyone needs a disc two please take it off my hands. I was always a console gamer I never played pc so I don't know the specifics. I think there is a version on steam. make offer. cleaning out my closet. I have a bunch of games taking up space. I want to possibly upgrade to a newer generation ( ps3, Xbox 360 on up) because I never had them growing up. I was fortunate and grateful enough to own a ps1, PS2, and original Xbox consoles.it was fun but it's time to move on. I would like these gone within the month if possible.