You can get it from the download page.
For details about the changes in Go 1.12, see the Go 1.12 release notes.
Some of the highlights include opt-in support for TLS 1.3, improved modules support (in preparation for being the default in Go 1.13), support for
windows/arm, and improved macOS & iOS forwards compatibility.
As always, we also want to thank everyone who contributed to this release by writing code, filing bugs, providing feedback, and/or testing the betas and release candidates.
Your contributions and diligence helped to ensure that Go 1.12 is as stable as possible.
That said, if you do notice any problems, please file an issue.
Enjoy the new release!