This page is not available in the language you have chosen. It will be displayed in English by default. If you would like to view it in a different language, you can try selecting another language.
Are you looking to make in-game UI? If so, the preferred method of making UI for your game is Unreal Motion Graphics (UMG).
Slate is the name for Unreal's custom UI programming framework. The editor interface is largely built using Slate.