The Ditto API can be currently be accessed using SOAP or simple REST requests.
You can get the metadata for the SOAP requests for a service by requesting it from http://api.ditto.net/{Service}.svc, e.g. http://api.ditto.net/Person.svc.
The REST endpoints are described in the documentation for each specific method. Presently REST endpoints only accept GET requests, as the exposed methods only provide access to read-only aspects of Ditto.
By default responses to REST requests come back in XML, but you can request a JSON response by specifying output=JSON in the request, e.g. http://api.ditto.net/rest/person/getcount?apiKey=xxx&output=JSON