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.)

> Is there any screenshots of the QEMU GUI running?

You are looking for Virt-manager or Boxes or any other GUI tool based on qemu if you want something similar to the vbox or vmware experience.

> it have software similar to Virtualbox's 'guest additions' software?

Yes, theyre called spice tools. Work for both linux and windows and infact pre installed on popular linux distros.

You're being unfairly downvoted, so allow me to actually answer your first question.

QEMU doesn't have much of a GUI to speak of. It's a virtualization framework with some CLI tooling on top of it. Frontends/management UI's/etc are left as an exercise to the community so you can find one that suits your needs.

For example, a popular one for macOS these days is UTM: https://mac.getutm.app

QtEmu is another: https://qtemu.org

There's virtio-fs, but it requires a relatively recent Linux kernel.

For Windows, I have samba running on my host.

QEMU does have a quite primitive GUI while it's running that lets you change disks and so on. But really, it's not a graphical emulator. You specify everything via command-line switches. (They're fairly intuitive, mind you. “-hda drive-c.img -m 16 -cpu 486 -soundhw sb16,adlib -vga cirrus” does what it sounds like.)

There are of course tools that provide a friendlier GUI wrapper if the command-line isn't your thing.

To pass files into VM I use lsyncd. It synchronizes changes to even big source trees over plain ssh and rsync. Of cause with big tree the initial copy takes time, but there is no security implications of exposing files to potentially untrusted VM.