Apache Tomcat is the container server which hosts the application. If you don't have Apache Tomcat installed, download it from http://tomcat.apache.org/download-80.cgi and follow their instructions. Apache Tomcat 7 is the minium required version.
3. Install the database
Skip this step when you're performing an upgrade.
PostgreSQL Skip this step when you're performing an upgrade.
Follow the PostgreSQL install guide to install and setup your database.