SOAP EN WSDL have something to do with xml, I dont recommend you to use xml either.
I recommend you to use json, because performance of json is better than xml.
I highly to recommend you to use volley https://developers.google.com/events/io/sessions/325304728
There are enough examples on the internet to make it work very well with your application!
However if you want to make a webservice see the question here > Android WSDL/SOAP service client
WSDL is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information. The operations and messages are described abstractly, and then bound to a concrete network protocol and message format to define an endpoint. Related concrete endpoints are combined into abstract endpoints (services). WSDL is extensible to allow description of endpoints and their messages regardless of what message formats or network protocols are used to communicate, however, the only bindings described in this document describe how to use WSDL in conjunction with SOAP 1.1, HTTP GET/POST, and MIME.
source:http://www.w3.org/TR/wsdl