This version of wxBasic is pretty crufty and stale. The most current version can be found on the Bleeding Edge page, which corrects a number of problems with this version and adds new features. The version found on this page is deprecated, and will be replaced once I get the documentation for the new version cleaned up.
Keep in mind that the code is still alpha - no warranty is expressed or implied, yada yada yada...
The wxWindows API is not included with the wxBasic documentation. It's available from the wxWindows site in a number of formats. wxBasic is built using the 2.3.2 release of wxWindows.