This is also answer to everybody else who was nitpicking...
I believe that OP ment a GUI front end when he said "no package manager". If he's running CentOS, then he has rpm installed, and most of his system (if not everything) was installed by rpm. I fail to understand why so many people are trying to be smart, instead of being helpfull. Luckily, at least Jay (haven't checked entire thread, maybe there were others) gave a helpfull answer (hint to the OP, "man rpm" contains answer to your question, as well as many other usefull options for rpm command).
You know, there's difference between "smart" and "smart ass". Nitpicking will more often get you closer to later then the former ;-)
Alexandar, he was asked the question in an interview, as far as we know not related to his CentOS system. Nobody, including the OP (and very possibly the interviewer) is really sure what the interviewer meant. I don't think anybody has been a "smart ass"