As it might be a little hard for you guys to find the places to go out, to experience Cologne Nightlife (which, indeed, has a lot to offer!), here are two links to webpages in english, which can give you a short overview of what possibilities there are to go out.

This one is a little more mainstream, concerning lots of clubs and locations in which also the music is more mainstream:

http://www.cologne.de/what-to-do/nightlife.html

This one also offers information about pubs, bars and a little more alternative clubs:

http://www.inyourpocket.com/germany/cologne/nightlife/clubs

And, in case your German is sufficient enough, this is always a good address to find something on short-notice or even on the long-run:

http://prinz.de/koeln/events/kategorie/party/

Hope you will have fun and enjoy your stay here!Â