Paros first crawl the entire website and than execute vulnerability tests, it is comes with an built in session ID analyser, you can generate a graph based on all the session IDS, it is also provides a built in fuzzer option. It is a great,simple and effective tool to use.
Paros Proxy Tutorial
Before installing paros you must have a java version 1.4 or above. As the name says this tool act as your local web proxy, so after installation you need to set up your browser on the local proxy. Open your browser network connection and on the proxy tab type.
After this all the traffic you male through your browser goes via this tool and the tool first analyse it.