Degree

Any non-profit organisation is nothing but group of people like we who really care about society and had that courage to push them self beyond the limits to bring the positive change everyone wants to see but not able to make it for many reasons. Glad to see that people nowadays are taking time to think beyond themselves and getting aware of their social responsibilities, though there are miles to go ahead in this field, but spreading awareness is good sign of near future. You have take a step ahead of the hudereds of people to go after thoughts to take social responsibility, best luck to you. As far as for qualifications there are no such education qualifications are required to join a NGO provided one has sound knowledge of a subject if opt for educational programs of a NGO, there are some NGO like teach India where one needs to apply for volunteering opportunities for which you got paid, If you are considering to work as an employment opportunity, it is really hard to name organisation here as it completely depends on individual organizational skills requirements for any open positions in their respective work area. As you mentioned that you lived in Kolkata, I would suggest you to joinBhumivolunteering organisation which is India's the largest volunteer organisation running across 20+ cities with different types initiatives like education for unprivileged kids, environmental issues, animal welfare and social awareness. You can opt for teaching under bhumi'sIgnitean educational programme where you teach to kids form diverse backgrounds such as orphanage centers, shelter homes etc. With a subject of your interest. Register yourself forBhumi volunteering opportunities here
Best luck & have great experience.