First you need to have a JCR repository running. The Explorer then expects you to have this repository available via JNDI. Then you need a version of the JCR-Explorer to deploy into your container. If you are at that point, access it via http://localhost:8080/jcr-explorer/login.jsf and use your JNDI name to log in.
Either check-out the latest sources (tagged version or snapshot) from the SVN repository or download the latest release of the sources. Then just build the WAR by executing 'mvn package' from the command line.
Binary release contain a file jcr-explorer.war, which can just be deployed into your container.
Be aware that these releases include bundled libraries. Depending on your environment you could wish to not have some the libraries included. Either remove them by hand from the WAR file (e.g. WinRAR can open the WAR file and allows you to remove single files manually) or try to build your own WAR file from the sources. In that case you can toggle including of the files by changing the scope of the relevant dependencies in the pom.xml to 'provided'.