USPS

Go to the Extensions → Shippings → USPS

If you offer USPS as a shipping option, your customers will see available USPS shipping rates at checkout, for delivery to their selected address.

Status: - MUST be "ON" for Shipping module to appear in your store.

Set extension status to ON, then USPS Settings button will appear. Click on it and fill in the following fields:

User ID: - Fill your USPS credentials in the User ID field. 

Password: - required

Zip Code: - Zip/Postal code of the starting location of your package.

Domestic Services: - select USPS domestic postage levels

International Services: - select USPS international services

Size: - Select the container size that you typically use to package the products ordered from your store.

Container: - Select the container type that you typically use to package the products ordered from your store. USPS will only deliver packages weighing up to 70 lbs.

Machinable: - It is recommended that you select Yes. Specify whether it is OK to handle your shipments by machines. Enabling this option reduces the shipping costs.

Dimensions: - Average package dimensions for shipping package.

Girth: - To find the girth of your package, measure the distance around the thickest part of the non-rectangular package.

Display Delivery Time: - Do you want to display the shipping time? (e.g. Ships within 3 to 5 days)

Display Delivery Weight: - Do you want to display the shipping weight? (e.g. Delivery Weight: 2.7674 Kgs)

Tax Class: - If you are required to charge tax on this item, select tax class

Location: - select the proper Location

Storefront Icon: - Shipping Icon to be displayed at checkout shipping selection

Auto Select: - You can set to skip shipping selection page if there is only one shipping option. This shipping method will be selected automatically

Accept these payments: - If only specific payment methods are needed for this shipping method, select them here. If nothing selected, all available payment methods will be shown