Before installing the XWiki WAR version listed here, you'll need to install a servlet container and a relational database, in this case Tomcat and PostgreSQL, following the instructions given.
After configuring XWiki (the concluding step), you will need to import the default skin for functionality. It can be downloaded at the same place as the WAR file.
The LDAP Authentication is basically straightforward. Replace the values with your own and you are set. LDAP users have to login to XWiki before they have a presence there. XWiki groups have to be assigned as the LDAP groups are not imported in.