For a service to be invoked, it usually requires request parameters. In this screen you can define one or more request parameters for the service. Every service will define different number request parameters. For example, for Twitter search service to work (http://search.twitter.com/search.json?q=), it requires a parameter named q. Some services don't require any request parameters. 

To enter one more request parameter, open Request Parameters panel. To add a new request parameter, enter its name in the input field and press the Add button.  Optionally, you can set its defualt value. This can be helpful when testing the service. To send a parameter in the head of the request, check Header check box. 

If a service requires one or more parameters to be part of the header, simply check Header check box for each parameters.