Catalina OS

There have been many changes between High Sierra and Catalina including many new features. The basic user experience is, however, much the same as what you are used to on High Sierra.

First you should check whether or not your Mac is compatible with Catalina -> macOS Catalina is compatible with these computers - Apple Support

Second, here are the instructions for downloading macOS -> How to download macOS - Apple Support

Third, make sure to back up all your user data to an external drive before you install or upgrade macOS.

I find Catalina to be very reliable and user friendly. It's not such a big change after upgrading from High Sierra.

I do prefer Catalina over most all older macOS versions.