The caveat, the host must have the network client setup configured correctly for Apex to work, which is the pinch point for most folks. For Windows, the user running the installer must be in the local Administrators group as well. As mentioned in the install prerequisites at http://docs.oracle.com/cd/E17781_01/install.112/e18803/toc.htm
A successful XE installation, with a running database and listener, as well as the proper services setup (windows) and all appears happy. Except the apex service does not start due to maybe an invalid %HOSTNAME% setting or something similar.
But there is in easy fix or workaround to that problem. Stop the listener and rename the ...network/admin/listener.ora file, or make the correct HOST= adjustment in listener.ora and start the listener. Done. ;)
Type http://127.0.0.1:8080/apex/f?p=4950 into your browser address bar. That's it, if the apex service is running.
Installer also creates a shortcut to the Apex page. Sometimes it doesn't get created exactly right, so I find making a few keystrokes much easier than digging around in a GUI for what ever I'm looking for. But then, maybe that's just me ... ;)
If you get a page error the installer may not have set the listener configuration exactly correct. There are numerous posts here on that particular problem.
Verify the database is running. Verify the listener is running. Verify that a `lsnrctl status` command has an endpoint with the ...presentation http ... port=8080 line. If you don't have all three apex web pages will not work.