I’m looking at http://reference.wolfram.com/language/guide/GeometricComputation.html and most topics, e.g. RegionIntersection, don’t have detailed description (no links). Does it mean they are not implemented yet?
If you are looking at functions for Mathematica 9, you can find them here: http://reference.wolfram.com/mathematica/guide/Mathematica.html
The website you are looking at does contain some functionality in its documentation which isn’t yet available. Some of the functions listed there don’t seem to be available in Mathematica 9.