You required to go through in Factories Act & Mines Act, where in all the welfare measures of workmen at work place defined. The role of welfare officer is to look into the facilities, and to facilitate those to workmen is prime. It doesn't sound good if you say that you have no knowledge about the function of a welfare officer. In general student used learn the function while pursuing the course and there is facility of internship in course curriculum while doing the course. The establishment decides the selection of welfare officer according to their choice from the staffs on role or new appointment with experience. In my knowledge no establishment recruits fresher for the post of welfare officer, since it is a statutory position. It would be better for you to if you can undergo some training in any factory or mines for some period(1-2 month).