You will need to download two tools -- the Blender2Ogre plug-in script (to create .xml files that are compatible with the Ogre representation of meshes) and the OgreCommandLineTools (to convert the xml files into the binary file format that ogre likes
Open up blender. From the file menu, select user preferences:
Select the Addons tab, and click Install from File
Navigate to the folder where you unzipped the blender2Ogre script, and select io_export_ogreDotScene.py
Press the "Install from File ..." button, and you then have a huge list of
addons you can install. Either search through all of these to find the Ogre one,
or type Ogre in the search field, and the click the square to activate this addon
You're done! Go back to the Quick and dirty blender tutorial and export away