Shiptheory integrates with Magento. Shiptheory will pick up any shipments that are created in your Magento store. Note a shipment is not the same as an order. Ie you may have an order for 10 items, and create 2 shipments for that order, on different days. Shiptheory handles each shipment differently.
Navigate to https://www.magentocommerce.com/magento-connect/developer/Shiptheory and select any of the extensions (note. the actual carrier configuration is handled inside your Shiptheory account, thus it doesn't matter which extension you install, all the extensions allow you to use all the carriers we support .
If you'd prefer to install the extension manually you can follow these instructions
You'll need to get your API key which can be found here
Once the extension is installed if you navigate to 'System' > 'Configuration'
From the left hand side select the Shiptheory extension and you'll see the Shiptheory setup box.
Make sure Enabled is set as Yes
Paste in the API key you got from here and hit the save config button (top right).
Once you've done this, you should start to see subsequent shipments you create show up in the 'all' tab in your shiptheory account
For a more detailed explanation of creating shipments in Magento, check this article here
You can also read about our more advanced Magento settings here : Advanced Magento settings in Shiptheory