It defaults to the GTK display: https://down.loaded.ie/Lb9RDi3.png. See the -display section in QEMU(1) for details and other options. My favorite is -nographic, which forces VGA output to the terminal; very useful when there is no X session or similar.
Edit: I realised GUI might mean creating and managing virtual machines; virt-manager might be good? Take a look at https://wiki.archlinux.org/index.php/Libvirt for the setup needed. (I think it's easier to learn to use vanilla QEMU, though.)
Edit: I realised GUI might mean creating and managing virtual machines; virt-manager might be good? Take a look at https://wiki.archlinux.org/index.php/Libvirt for the setup needed. (I think it's easier to learn to use vanilla QEMU, though.)