1. The boot menu showed an option to boot UEFI from the CD-ROM.
2. I selected UEFI.
3. I clicked through installation of Debian with default settings, noticing that Debian made UEFI boot partition.
4. I rebooted the computer and everything worked (except sounds, but that's another issue).
5. I upgraded the kernel to fix sound issue and to see can Debian upgrade the kernel without messing UEFI.
6. I Rebooted and the sounds worked with the new libre kernel.
Conclusion: For a normal user UEFI can be at the moment with the Gigabyte mobo/BIOS very trivial and simple.