Thank you for downloading JIRA 3.1.1 - Standalone distribution. This distribution comes with a built-in Tomcat 4.1.29 web server and hsql database, so it runs (almost) out the box.
Install a Java Development Kit (JDK) from http://java.sun.com/j2se/downloads.html. Sun's page is a bit confusing — avoid the Netbeans and J2EE sections and get the J2SE JDK.
More documentation is available online at:
http://www.atlassian.com/software/jira/docs/v3.1.1/install.html
A common startup problem is when another program has claimed port 8080, which JIRA is configured to run on by default. To avoid this port conflict, JIRA's port can be changed in conf/server.xml.
If you encounter any errors, please report them to the jira-user mailing list, or contact Atlassian directly at support@atlassian.com
Questions? Try the online documentation or ask on the mailing list