The new macOS High Sierra 10.13.2 beta can be downloaded from the Apple Developer Center or through the Software Update mechanism in the Mac App Store with the proper profile installed.
It's not yet clear what improvements the second major update to macOS High Sierra will bring, but it's likely to include bug fixes and performance improvements for issues that weren't addressed in macOS High Sierra 10.13.1.
This update may fix a serious macOS vulnerability that enables the root superuser on a Mac with no password or additional security check. Apple released a patch for the bug in macOS 10.31.1, but the issue has not been fixed as of yet in macOS 10.3.2.
No significant new features were discovered in the first five betas of macOS High Sierra 10.13.2, but we'll update this post should notable changes be found in the sixth beta.
Update: Today's macOs High Sierra 10.13.2 beta is also available for public beta testers.