Liferay is a web portal system. Liferay is JSR 168 compliant. Liferay is implemented as a java compliant web application. Liferay is typically installed as a root context in Tomcat. More popular installation packages of Liferay come with a bundled tomcat. Although that is technically true, the download instead contains a tomcat with a preinstalled Liferay as its root context.
Installing Liferay involves unzipping this tomcat and starting the tomcat from the tomcat bin directory. The only real prerequisite is that there is a jdk installed and java_home set. Subsequently you can see Liferay in action by going to
http://localhost:8080
The default view of this site is for users or guests that haven't logged in yet. This is the public face of the portal web site. Liferay comes with a built in test user for testing the sign in process. One can also sign up for an account. Once installed the portal can be configured using its internal portlets and themes.
The out-of-the box Liferay comes with hypersonic sql. Nevertheless it is highly advisable to use mysql as soon as possible. The main issue you will run into otherwise is that you may not find good tools to manipulate the database.
This document will cover the basic mysql installation as well and also running command line prompt for mysql and using the mysql tools for such things as creating the database etc.