If USPS W2s are configured in ESS, employees will have the ability to query their W2. Once a specific W2 is queried, you to download a PDF version of it or open (view) it in PDF format. Viewing a W2 will open it in another tab that you can exit out of when you are finished viewing it.
More Information on View/Print W2
Users with Administrator Role have the option under System>Configuration>ESS Functionality Configuration to turn on/off View/Print W2 option.