Shipping Integration is an addon for Store Manager for Zen Cart which allows you to handle USPS shipping by printing postal shipping labels directly from your Store Manager.
You can find general information on the addon and its trial version here - http://www.zencart-manager.com/shipping-integration
Documentation with step-by-step manuals which explain how to perform main operations is available at: http://shipping-integration-documentation.emagicone.com/
If you have any specific questions on the product, post them here and we will gladly answer them.