Возвращаться and вернуться are imperfective and perfective forms of the verb, accordingly. To understand how to use them properly, you need to learn about verb aspects in Russian, here for example: http://learnrussian.rt.com/grammar-tables/aspects-of-russian-verbs--imperfective-and-perfective/

"Вернуться" is mostly used in the Past and Future Tense (Perfect): я вернулся (I came back), он вернётся (he'll come back). "Возвращаться" is mostly used in the Present: я возвращаюсь завтра утром (I'm coming back tomorrow morning). "Возвращаться" can also be used in the Past Tense (Imperfect): когда я возвращался домой, пошел дождь (when I was coming back home, it rained).

Возвращаться it is returning Вернуться it has returned Возвратиться it had returned