Tracking USPS packages by entering tracking number on official site : USPS Tracking
USPS Tracking with a Shipping Label
In most cases, when you print a shipping label for a package with Stamps.com, you will automatically receive USPS Tracking free of charge. Note that First Class Large Envelope will not include USPS Tracking. To do this:
Click Packages in the left navigation bar in the software or Print Postage in the top navigation bar of the website. Enter the addresses, mailpiece info, and mail class. In the Tracking drop-down, select "USPS Tracking". With USPS Tracking you can drop your item in any mail collection box, hand it to your letter carrier, a retail clerk, or schedule a free USPS pickup.