GetPage literally does that - it gets a page by name. It returns everything about that page in a hash format.
Page - This is the name of the page that you wish to retrieve.
Revision - Optional, this is the revision number of the page you wish to retrieve. If undefined, GetPage will retrieve the most recent revision.
These are actual examples from the Aneuch source code:
my %F = GetPage(GetParam('page'),GetParam('revision',''));
Here, the hash %F will be populated with all page data from GetParam('page'), and if a revision is defined then it will pull that specific revision.