Unlike the previously released OS X El Capitan Beta 4, Apple hasn't listed or announced any new features and changes brought by OS X El Capitan Beta 5, suggesting that the fifth build of OS X El Capitan is a minor one featuring enhancement to the operating system, under-the-hood performance improvements, as well as bug fixes.
You can get OS X El Capitan Beta 5 through Software Update or via the Mac Dev Center for registered devs.