Consuming SAP PI Webservices/API

Hi,

Is there any tutorial regarding the consumption of SAP PI APIs/Webservices? I have found a lot using external APIs but not within SAP.

For example, I have WSDL url, but the WS has 5 operations. I want to try using one of the operations. It then asks for the SAP user and password. My request would be in XML form.

Thanks.