Originally dubbed the 'April 2019' update before an extra month of testing was deemed needed by Microsoft, Zac Bowden has done a nice overview here in video form, if you want to be led through what's new over your morning tea of coffee:
He's also done a complete changelog here on WC. In summary, there are a truck load of blur and acrylic UI effects, Search and Cortana are now totally separate, many of the Microsoft applications can be uninstalled if needed, the Start launcher is now its own process and so is less likely to be compromised if another app malfunctions, plus Windows Update has been improved in many ways, not least by reserving itself 7GB of workspace to avoid storage issues.
If you are ready to install the update now, then open 'Settings > Update & Security > Windows Update' and select 'Check for updates'. If this doesn't work then you can force the update via the Update Assitant.