Where do i enter im head of household?

When you begin your return TurboTax will suggest the appropriate filing status based on your answers in the interview. 

You do not enter you are Head of Household.  

You select your filing status as Single or Married but not including your spouse on the return.

When you are entering your personal information in the My Info section of the program you must have a qualifying person as a dependent on your return.  The program will ask you a series of questions to determine if you are eligible for Head of Household.

If you do not have a dependent then those questions will not even be asked since you are automatically ineligible for Head of Household