Processes are generally started using a business service/page-flow concept in TIBCO AMX BPM.
A page flow is nothing but a simple 1 or more page web application that internally spwans your business process instance.
In case you do not want to use page flow processes and would like to directly start the business process, you need to make use of the 'Start Process Instance' button that is available in TIBCO AMX BPM workspace. [More]