Original: Kölsch is one of the very few only city dialect in Germany, besides for example the one in Berlin ("Berliner Schnauze").
Simplified: Take the beginning from "kernel" or "colonel"; next take a real dark, long "l" as in "bold", or "ball"; then append a "sh" as in "shrimps", or "ti" as in "nation". That's the sound "Kölsch". However, the German "ö" is not exactly the same as an English "o", but a sound between "o" and "e".