Hi Abdul,
Once you create a web service, it will will generate a WSDL file using t-code SOAMANAGER. This file can be used to communicate with 3rd applications.
Also, have a look on below links,
http://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=226165233
http://help.sap.com/saphelp_nw04/helpdata/en/9b/dad1ae3908ee44a5caf57e10918be9/content.htm
Thanks
Abhi