To see all the modules available in your domain, from the left navigation area of the administration interface near the top, click Modules. The list, which may be several screens long, shows all the modules. To see just the modules of one type select that type from the Features list, and click Go.
Let's say you have purchased a shipping module designed to calculate rates for a new shipping company. There are a few simple steps to take so that you can begin using it:
After purchasing the MIVA Merchant 5 module, download it to your computer. If it was supplied as a Zip file, unzip it to a convenient directory.
Many modules provide documentation. This will be included in the Zip file. If installation instructions are included with the module, use those instructions.
Go to the Modules screen in the administration interface, and click Add Module. Upload the file to your server just as you would upload an image, or other file.
Once you have uploaded the module to the server, it will appear in the domain–level modules list.
Go to the store feature that will use the module and select it from the list. In the case of the new shipping module, you would click Shipping Configuration. The new module will appear in the list there. Select it and click Update to assign it to the store. You can begin using it in the store immediately.