ABAP Webservice

Hi Experts

I understood that ABAP Function module can be exposed as webservice. My question is after creating the webservice out of Function module in SAP then how the 3rd party or Non-SAP system will access it. What are the other activity that we need to perform in SAP system other than creating a Webservice out of Function module. Also what are the details that we need to share with 3rd party or Non-SAP system developers. We are not having any middleware in our system landscape.

Thanks

Abdul Hakim