But EPubCheck doesn’t work like a regular program, instead it’s a java program that you’ll need to run from a command line. First go to Google Code to download a copy of EPubCheck. You may have to extract it but chances are your OS or browser will automatically do so. Then get to a command prompt where you can type in:
java -jar epubcheck1-2.jar file.epub
In the above, epubcheck1-2.jar refers to the exact file name of the validator you just downloaded (obviously different if you’ve downloaded a more recent validator) and file.epub the name of your epub file.
Mac OS X
This process is easiest on Mac OS X where you almost certainly have Java installed. Just fire up Terminal (you’ll find it in the Utilities folder of your Applications folder) and type in "java -jar " — remember to type the space after "-jar " and then drag to the terminal window first the validator you downloaded and then your EPUB. By dragging the icons of these files, you don’t need to type in the files and most importantly the convoluted paths to these files. Then hit return and the validator will run and hopefully tell you there are no errors.
This is a little more complicated if you’re using Windows because you might not have Java installed and if that is the situation, find instructions here: http://www.java.com/en/download/help/windows_manual_download.xml
After you’ve installed Java, you can still do the trick of choosing the Run command from the Windows start menu (click here if you can’t see the Run Command), typing "java -jar " and then similarly dragging and dropping the validator and the EPUB to the Run command line.
There are further instructions for installing and running EPubCheck here: http://blog.threepress.org/2010/12/16/running-epubcheck-on-your-computer/
Windows users running Apache Tomcat can also try installing EPubCheck as an application, see instructions here: http://code.google.com/p/epubcheck/wiki/WebRunning