Vrat and Upavas are nothing but synonyms of Fasting. In Hindu Culture, Vrat is performed by people to please God and ancestors. It is believed that you can wish anything from Gods but you need to show your love for him too. Vrats and Fastings are one way of showing your submission to Almighty. In Hinduism, the method to perform Fasting is described.
Most people do Vrat on Purnima, Ekadashi, Pradosh, and Sankashti days of Hindu lunar month. Likewise, there are other Fasting dates followed by some.
Ekadashi Upavas is done to please God Vishnu. Vishnu is the God responsible to feed all lives and Ekadashi Fasting is done to desire long happy life and health. Pradosh Fasting is done to please Hindi God Shiva and most people do it to get a beautiful life partner, marital happiness, compatibility, and overall happy life. Sankashti Upavas is dedicated to God Ganesha and means the destruction of Sankat (Problems). Sankashti fasting is done to get rid of problems and most it to get out of difficult life problems.