If your employer is a TurboTax partner then after you put in their 9-digit Employer ID number you'll be walked through the steps to import.
If your employer is not a TurboTax partner then importing this way is not an option and you can enter your W-2 info manually, or if you are working with TurboTax Online you can snap a photo of your W-2 using the TurboTax Mobile App (https://ttlc.intuit.com/questions/1934390-how-do-i-import-my-w-2).