The film is based on an older Indian novel. It's a very sentimental star-crossed lovers story set in 1930s India: Devdas and Parvati have been in love for ages but can't marry. Parvati is instead married off to an older man. Devdas turns to drink and a dissolute life, which introduces him to the courtesan Chandramukhi. She falls in love with him, but he is unable to fully reciprocate. Devdas eventually drinks himself into a tragic ending.
In the Maar Daala number, Chandramukhi bets with another of her patrons on whether or not Devdas will show up that evening. When he does, she performs this number.
Unfortunately, the best quality video I could find has no subtitles: