Invoke a web service through the internet

hi,

after reading a lot about the NetWeaver i understand the it is possible to invoke a web service through the internet,

i am attempting to do so using the SAP BC,

i understand that it is possible to write a web service using the SAP BC Integrator but all i need to do is to invoke an already written web service,

i should say that i have never before worked with this technology (web services),

thnks,

mickey.