Lightroom Classic is the upgrade/replacement for Lightroom 6. It is the current version of Lightroom that keeps all of your images ON your computer and functions the way you are accustomed to having Lightroom 6 function. When you install Lightroom Classic it will create a new copy of the catalog you have been using with Lightroom 6, leaving the old catalog intact. When Lightroom Classic opens, using the new version of the catalog, you should be able to resume using Lightroom Classic at the point you were in Lightroom 6.
Using Lightroom Classic, you will have the capability to create collections of images that you can choose to share as smart previews that can be shown on your mobile devices and other computers. They can even be edited with the mobile apps that are available.