You need to have a degree in social work and get urself registered with Singapore Association of Social Workers, before u can be recognized as a social worker in Singapore and earn a good salary. Social work is increasing in popularity and there's waiting list for school admission so do plan ahead and plan well.
Can start with volunteering at social service agencies to know what they do on a day to day basis
Different agencies, diferent work style and processes. Some are more centre based while some others are more active in institutioks or community-based. Depends on the target clients you would like to work with too.