If you are holding a Long Term Visit Pass issued by the Ministry of Manpower, you will need to get a work pass to work in Singapore.
You first need to get a job offer in Singapore, then get your prospective employer to apply for an Employment Pass, S Pass or Work Permit for you. You will have to meet all the criteria for the pass that your employer is applying for.
You are not allowed to work in objectionable occupations such as a dance hostess or a masseur.