go to Site Settings and set registration type to "verified" (users need to enter verification code from confirmation email) or private (admin has to authorize users).

Thank you buddy but dear i am confused between the funda of registered user and authorised user  if i keep my registration process verified aur private unless i dont authorise user it doesnot get access to the portal he cannot login givess password error,even in private unless i do authorised user it does not allow the user to login. i want my users to only access forum through login nothing else on my website requires authentication plss help me which registration mode should i keep and what should be the user settings.help would really be appreciated guys