Follow the headline link to take Apple’s official Catalina tour. You’ll likely want to click or tap one of the arrows at some point, just to switch the tour to manual. Makes it much easier to follow. But worth stepping through.
I love that this works fine on your iOS device, or on an older version of macOS. Gives you a chance to learn, without committing to the install. Be sure to click the + when it appears on a page to learn more.