Sith holocrons hold knowledge and wisdom that can only be accessed by dark side practitioners. The artifacts can also be used as keys to unlock temple doors. The Sith temple on Malachor was the home of a Sith holocron that Maul attempted to steal with the help of Ezra Bridger. When placed in the temple's obelisk, the holocron could create a super weapon, designed to take life. Maul's plans were foiled, however, when Ezra and his Master Kanan were able to pull the holocron from the obelisk just in time.
After the events on Malachor, Ezra opened and used the Sith holocron -- in secret. He was on a quest for more power, and would consult with the holocron for guidance. When Kanan discovered this, however, he took it away from his Padawan. Eventually, Kanan gave the artifact to the Bendu, an ancient being strong with the Force.