This layout feature "rolling umlauts". Typing ae, oe, ue, sz respectively gets recognized and spits out ä, ö, ü, ß. For this, your systems keyboard layout/language has to be set to DE/German
The layout is also designed around a rotary encoder in the top left corner that switches between slow and fast scrolling in the default layer by pressing it down while turning. In the numpad layer it scrolls left/right and pressing it down holds shift to select while scrolling.