Download tomcat specific war file from maven repository and in kie-wb-distribution-wars-6.2.0.Final-tomcat7.war/README.txt you can see all the instructions to deploy this war file in tomcat server.
Thank you for the quick reply. Now I use jbpm-designer(droolsjbpm/jbpm-designer · GitHub) ,because I need the bpmn2 web editor only. Moreover, could you please suggest me some document to read in order to help me get familiar with the code faster? THX!!