For this you have to be sub-broker ( this is in case of BSE/NSE cash ) or Authorised Person ( this is in case of F &O) and have few clients mapped under you. But this will require SEBI registration, payment of sub-broker fees , acceptance by main broker and also you will come under inspection /and other regulations of the broker,The Exchange, SEBI etc. It will need NCFM exam certificate also.
If you are managing trades/money for few family members/close relatives then it is ok but if doing for public, it is illegal unless you have portfolio managers registration from SEBI ( this needs large networth of some 50 Cr ). If things go bad and someone complains to SEBI, your main broker and you will come under serious trouble. Many are doing it but the problem comes only when things go sour. Cautioning because I know many cases where police went after such money managers and they have to run away to save police harrassment.Police considers it as cheating under section 420 of IPC and is a criminal offence.
Smart_trade