You can ask your employer or payroll department if they provide a website for employees to download their W-2's. Your employer's W-2's may or may not be available yet.
You may be able to import the W-2 into TurboTax even before you get a copy--if the employer participates in the import program with TurboTax. But often one needs a verification code to use for importing or other verifying info that is on the actual W-2. See this FAQ:
https://ttlc.intuit.com/questions/2580775-will-i-be-able-to-import-my-w-2-before-i-get-it-in-the-mai...
