German Zeppelins during World War I were principally used in attacks on British, French, and Belgian cities with bombs, as well as providing naval reconnaissance and patrols for the German High Seas Fleet. Early in the war, these airships were almost invulnerable while attacking London and other cities, because they were able to climb much higher than the weak engines of contemporary aircraft could go, and it was very difficult to intercept them and shoot them down. However, aircraft technology quickly advanced during the war, and soon it became dangerous for the Zeppelins to operate under risk of attack by fighter aircraft. Castles of Steel by Robert Massie is a good book about the use of Zeppelins for patrol and early warning in the North Sea naval campaign, while The Zeppelin in Combat by Douglas Robinson is a good book about the air raids and city attacks.

I don't believe any of the surviving rigid airships / Zeppelins were actively used in World War II, but several air forces, including the Americans, used blimps for maritime patrol. These blimps would take long patrols loitering over Allied convoys and shipping lanes, looking for and attacking German submarines, often with MAD (Magnetic Anomaly Detection) gear. These blimps could slowly loiter for a much longer time than aircraft, and were used right up until the end of the war in this coastal anti-submarine role. One of these blimps, K-74, was shot down by U-134 while it was attacking it. The last German submarine sunk during the war, U-853, involved search and attacks by US Navy blimps.

EDIT: Here is an example of one of the US Navy blimps