For the different products inside EBS you find the different gateways. Most of them have a WSDL.
I won't give a complete run through demo as I'm currently working with HR and I didn't see an XML Gateway for that. Nevertheless I will tell you how I would do it.
In APEX go to Shared Components > Logic > Web Service References.
Create a new Webservice based on a WSDL (the one you selected from the EBS Integration Repository)