No I’m not talking about the pickelhelm, I mean the M1916 Stalheh. The small horn like things on the sides of their helmets. What were they and what did they do?
Those "horns" on the side, are for the purposes of ventilation and to support a a steel brow plate for extra protection. It was later dropped because the brow plate made the helmet too heavy for general use.
Bull, Stephen; Hook, Adam (2002). World War I Trench Warfare: 1914–16. Osprey Publishing. pp. 10–11
The little "horns" on the side of German WWI helmet were used to hold a slotted, curved steel plate which covered the front (forehead area) of the helmet. Contrary to (some) popular belief, a steel helmet will not stop a high velocity rifle bullet. The plate could stop or at least deflect a bullet when a German soldier stuck his head up out of a trench.