For documentation on specific classes, see the perldoc for the class. There is a list below of classes currently wrapped. The documentation for each class is somewhat minimal. In the DESCRIPTION section there will be a link to the corresponding C++ API documentation on the OGRE website. The documentation of methods uses C++ types to describe its parameters and return values, so some translation to Perl is generally required.
Not all methods are currently wrapped, although there are enough to run the examples, which isn't bad. But expect to find that your favorite method isn't wrapped yet. I'm working on completely wrapping the methods, but it's still not there. One particular "category" of methods not yet wrapped is those that return a C++ reference, rather than a pointer (one exception is Node::getPosition). Methods that return fundamental types, like bool or int, are usually wrapped, provided their arguments aren't too weird. There are also some overloaded C++ methods (i.e. different argument parameter types but the same method name) that have only one version of that method implemented; I have to work on how to handle that.
See TODO.txt for more things that aren't done yet.