See the documentation.
The plugins video (http://dl.dropbox.com/u/4958764/docathon/installing%20plugins.mov) has captions and audio. This is a slightly outdated video as it shows how to install Service Catalogue plugin in Taverna Workbench. Service Catalogue Perspective is now an integral part of the Workbench Enterprise.
If the Workbench for your specific domain, e.g. astronomy or digital preservation, does not have this Perspective - you can still install it as a separate plugin. Please refer to the video on installing plugins to see how to add the Service Catalogue plugin to the Taverna Workbench. The Service Catalogue Perspective allows you to access the vast content of the BioCatalogue Web Service registry (and its other instances such as Biodiversity Catalogue) from the Workbench.
By typing a search term into the search box, we can instantly access the results and view the associated service and service provider data. An example of this search could include the word "KEGG". This would return a number of results. Clicking on the "Kegg" service, int he services tab pops up a window that contains detailed information about the service, including: the service submitter; the status of the service (whether it is down or not); and any example data or descriptions that would help a researcher use the service in one of their workflows. Similarly, a clicking on the DDBJ tag in the tag cloud also brings up a detailed information window.
We can also add a service directly into the Taverna Workbench by simply clicking on the small window button with a " + " in the top left of the icon (located on the far right of the bottom right panel of the pop-up window - above the star icon). If you navigate back to the design perspective, you should now see the added service in the Workflow Diagram and Workflow Explorer panels. You can now freely integrate this service into the remainder of your workflow as you would a normal service.