You can get good tranining material and examples from http://salaboy.wordpress.com/2011/01/24/announcing-jbpm5-community-training/
1) I want to create a new bpmn process and deploy that using Eclipse. I have created the process but am not sure of the deployment procedure. What is the procedure to be followed?
It depends on how you want to deploy the bpmn process. It can either be deployed in JBPM web console and use the ftl forms for user tasks. Alternately, you can also deploy the bpmn in the container of your choice and access BPM engine using your preferred front end (e.g Flex, GWT, JSP, RCP, Swing etc).
If you are planning to deploy in JBPM5 console, here are a couple of simple examples as a starting point.
http://community.jboss.org/people/bpmn2user/blog/2011/02/27/jbpm5-console--hello-process-example
http://community.jboss.org/people/bpmn2user/blog/2011/02/21/jbpm5-example-for-forms-with-variables
2) How do I add new users and groups to the system?
See this discussion http://community.jboss.org/thread/161982
Also see some examples from the source code (http://sourceforge.net/projects/jbpm/files/jBPM%205/jbpm-5.0-Final/ or from GITHUB https://github.com/krisv/jbpm/tree/master/jbpm-human-task/src/test)
You might find the api (taskSession.addUser(user), taskSession.addGroup(group) etc) useful.
3) I am not able to open the reports, the attached error is thrown in the jbpm-console. How to I start the report server?
The report engine is embedded (i.e., you do not need to start the BIRT report engine seperately) and if the install is successful, you should see the reports.