Armies of Anubis can be accessed by running south of Home until you see Sphox's pyramid. Once there you will click the left Jackal statue and you will be moved to the Armies of Anubis lobby.
Armies of Anubis has 5 rooms of challenges. The first 3 rooms have 3 waves of monsters each, with the 4th and 5th rooms having only 1 monster.