After you file

You do not enter a W-9 on a tax return.   What are you trying to enter?   Do you have self-employment income?  Did someone give you a W-9 to fill out so they can issue a 1099NEC to you?  

https://ttlc.intuit.com/community/forms/help/what-is-a-w-9-and-what-do-i-do-with-it/00/26161

If you have self-employment income:

SELF EMPLOYMENT INCOME/“side jobs”

https://ttlc.intuit.com/questions/2926899-how-does-my-side-job-affect-my-taxes

https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/...

https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922

https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax

https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c

https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct

https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs