You can apply for a Letter of Consent to work in Singapore if you are an eligible Dependant’s Pass holder, or an LTVP/LTVP+ holder who is the spouse or unmarried child of a Singaporean or permanent resident.
This is an official document (LOC) given by the Ministry of Manpower (MOM) to permit qualified Dependant Pass, Long Term Visit Pass (LTVP) or Long-Term Visit Pass Plus (LTVP+) holders to look for employment.
However, if you want to start a business, you should apply for Employment Pass instead.