If USPS payslips are configured in ESS, employees will have the ability to query a payslip by pay date or check number. Once a specific W2 is queried, you have the option to download 
a PDF version of your payslip or open (view) 
it in PDF format. Viewing a payslip will open the payslip in another tab that you can exit out of when you are finished viewing it.
More Information on View/Print Payslip
Users with Administrator Role have the option under System>Configuration>ESS Functionality Configuration to turn on/off the View/Print Payslip option.