2. Get an Amazon Web Services Access Key and Security Key
In order to run this sort of web service on your site, you will need to register for an API called Amazon Web Services Access Key. This will allow you access to customize and display a range of Amazon products on your site. More importantly, you need it for the plugin to work.
You can get your access key from Amazon Web Services by joining the community at http://aws.amazon.com. You’ll be given an AWS key to use in all your web service requests after you register.
3. Upload the Plugin Files
Add through repository or the WP-Admin plugin upload feature and upload the amazonpress.zip file.
or Unzip and upload the /amazonpress/ folder and files to your WordPress plugins folder, located in your WordPress install under /wp-content/plugins/
4. Activate the Plugin
Browse in the WordPress admin interface to the plugin activation page and activate the AmazonPress plugin.
5. Configure Management Options
The plugin should now be installed and activated however no products will be displayed on your site quite yet. The first time you visit management page, the appropriate tables will be created in the database if necessary.
On this page you will need to enter the Amazon Associates Tag and Amazon Web Services Access Key you registered for above. You can also configure various aspects of how the plugin functions such as the number of results to show, and so on.
Once you save these options, the products will begin to be displayed on your site related to the topics of your posts.
In WordPress 2.7.x and higher, the AmazonPress management page is located under the Tools menu on the left hand side of the WordPress admin interface. In WordPress versions before 2.7 it is located on the AmazonPress page under the Management TAB along the top of the admin navigation.