Ok, so you are trying PAAS (Perl as a Service). And you are not using a RESTful interface to do that. What do you have? Basic perl where you need to write your own webserver? An Apache webserver where you can put CGI-BIN's in? A Plack/Dancer2?

If you have an apache webserver, that allows CGI's in your home directory... then read "Writing a CGI program" at Apache docs - cgi

Get that first running.

edit: Here is a very good Perl CGI tutorial: perl_cgi

Once you mastered that, throw SOAP into the mix (scroll down to the examples first, or you head will overload and explode): SOAP::Lite

If you are interested in theory and alternative methods: modern ways of doing web services