In the window design the map with your stations, missions and moving vehicles covers the whole screen. You have buttons on the bottom which you can use to access mission list, your station list chat and radio.
 
Using window design you have a more immersive experience by playing on a bigger map. You have full control over the menus, you can move them to where you want to have them and change their size or hide them completely, according to what you need.
 
To use window design go to the settings in the main menu and the “miscellaneous” tab. You can also choose a dark mode version of the window design.