Hi Tengh, welcome to the Forums 
The Homescreen is one Mycroft Skill that has a GUI and it’s what is shown by default on the Mark II when nothing else is happening.
Mycroft-gui is the Qt display framework - it sits behind the scenes and is what translates the code in Skills like the Homescreen to actually display things on the screen.
We haven’t been doing any work to bring the GUI to Picroft just yet as we’re focused on getting the Mark II out to everyone as soon as possible. If you want to try get it running on the Pi, you can install it using the same steps as for mycroft-core but using this repository: