it should be easy, on the slashscreen move the mouse to the start text and press quit. If you in a project, move mouse to the left-upper most side of the screen, close project, move mouse to start text and lastly click on quit.
Move mouse or arrow keys to start text > click on quit
If in a project move mouse or arrow keys to left-upper most side of the screen > click on close project > move mouse or arrow keys to the start text > click on quit