Why is my federal tax refund 0

No one in the user forum can see your tax return so we cannot tell you why you have no refund.  Did you enter taxable income with tax withheld?  What income did you enter?  Did you double check all of the amounts you entered?

And...

You are posting from TurboTax Live.  You can arrange for the Live help you are paying the extra fee for with your questions from  5 a.m. to 5 p.m. Pacific time  Monday- Friday

https://ttlc.intuit.com/questions/4124827-how-do-i-connect-with-a-tax-expert-in-turbotax-live

Have you filed already?   Did you maybe click on Amend to get back into your return?  Amending resets your refund to zero to start filling out the 1040X Amended return.

Or at the end did you accidentally say to apply your refund to next year as an estimated payment on line 22?