You will need an EGL Service part, as well as a requester that has binding information for accessing the service.
The simplest way to debug a service is to call it from a program in the same project as the service. You can then pass test values to the service and inspect the results.
program addTestProgram type BasicProgram myAddingMachine additionService {@BindService {bindingKey = "additionService"}}; function main() sumint int; sumint = myAddingMachine.addInts(5, 12); SysLib.writeStdOut("result = " + sumint); end end