Apart from the free trial mentioned by sqrt17 (orange "Get started free" button at http://bluemix.com/), you can find open source (Apache 2.0) SDKs for different languages.
It was useful to read the source code to figure out some aspects I didn't find in the documentation.
get a free 30-day trial of Bluemix. The Watson tools are accessible through Bluemix and there's a free tier that allows you to try out things for yourself.