To build your package in Guvnor, you have to add your model jars to it. For that in the top-left "Create New" menu select "Upload Pojo model jar" and name it and upload your jar.
Note that jar files are not part of the compiled package (pkg) that Guvnor creates when you build a package and exposes it to your clients.
You have to also have your model jar on the clients classpath.
If you are using jbpm installer and testing execution of your processes in the jbpm console, easiest thing to do is to place your model jars in the $installer/dependencies directory and run
ant clean.demo
ant install.demo (or ant install.demo.noeclipse)
and start.demo
installer then will place your model jars in the right places for you for console.
HTH