Look into the export menu of your Blender installation. If it does not export to Ogre Mesh/Ogre DotScene yet, it's time to install a free plugin from ogre3d.org. There you also find plugins for other 3D modeling tools.
The jMonkeyEngine SDK assists you in installing the Ogre XML plugin into Blender 2.63+, so you can follow the examples in this book:
In the top-right search box of the jMonkeyEngine SDK, type "Install Blender Ogre XML".
A list of the actions and help resources appears. Select the "Install Blender Ogre XML" action and press Enter. A dialog box opens.
Click on change to set the path. Browse to your Blender script directory and click on OK. The default paths in various operating systems are as follows:
Windows 7 – C:\Users\%username%\AppData\Roaming\Blender Foundation\Blender\2.63\scripts\ Windows XP – C:\Documents and Settings\%username%\Application Data\Blender Foundation\Blender\2.63\scripts\ Mac OS X – /Applications/Blender...