The macOS High Sierra update improves the stability, performance, and security of your Mac, and is recommended for all users.
This update adds support for Messages in iCloud, which lets you store messages with their attachments in iCloud and free up space on your Mac. To enable Messages in iCloud, go to Preference sin MEssages, click Accounts, then select "Enable Messages in iCloud".
For more detailed information about this update, please visit: https://support.apple.com/kb/HT208723
For detailed information about the security content of this update, please visit: https://support.apple.com/kb/HT201222
You can download the macOS High Sierra 10.13.5 update from the Mac App Store. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.