Beta testers who have signed up for Apple's beta testing program will be able to download the new macOS High Sierra beta through the Software Update mechanism in the Mac App Store.
Those who want to be a part of Apple's beta testing program can sign up to participate through the beta testing website, which gives users access to iOS, macOS, and tvOS betas.
macOS High Sierra 10.13.2 appears to focus primarily on bug fixes, performance improvements, security enhancements, and other under-the-hood updates. No major outward-facing features were found in the first two developer betas.
The previous update, macOS High Sierra 10.13.1, addressed a serious WPA 2 vulnerability and introduced new emoji.