Complex sentence: It is also believed that Uttara had learnt dance from Arjuna as a princess during the 13th year of exile of the Pandavas in Virata's kingdom when Arjuna lived a life of a eunuch and practised his art of dance learnt from the apsaras in heaven.
Split into simpler sentences: It is also believed that Uttara had learnt dance from Arjuna during the Pandavas'year of exile-in the Virata's kingdom. Living incognito, as was the term of the banishment, Arjuna lived a life of a eunuch and practiced his art of dance learnt from the apsaras in heaven.