Hi vicsdriveinn,
I'll share the reference with detailed steps to enter your employees historical data.
You'll want to enter their transactions (prior payroll) in QuickBooks, so you can generate their W-2 forms. Please refer to this article: Set up a prior payroll.
When it's time to create the W-2 forms, please refer to this article: File W-2 forms.
If you have additional questions, you can always go back to this thread.