Outside of war, they were used as lush people transports (watch Indiana Jones and the Last Crusade for an entertaining scene, and the Hindenburg disaster for a not so entertaing real life one.) Probably cargo too, but I've never looked into it.

They were quite useful in wartime, especially at the beginning of the war. They were used for recon and bombing runs. The Zeppelin was a particularly fearsome beast, that had huge psychological effects on the enemy (they could be heard, but not seen, raining death from above). They could fly significantly higher than planes of the time and at the beginning, planes didn't have great guns to shoot them (or anything) down. Even if they were hit, bullets would pass right through, even though they were filled with hydrogen, because there was no spark/flame involved. Anti-aircraft spotters and guns also weren't super effective for Zeps, especially at night.

That all changed with the invention of incendiary and explosive bullets. A single shot could take down a Zep in a great, flaming ball of fire. That, along with improved guns and higher flying aircraft pretty much ended the time of the Zeppelin. I think by 1917, they were all but obsolete for war ops.

This was the R33-class airship. This was actually used for military air support and these airplanes would be deployed midair! Crazy madlads

Later it would be used for prototype mooring testing and traffic reporting