If you are on a Windows 10 machine you need to setup WSL with a distro of your choosing. When you have WSL ready or you are on a Linux machine you should update your packages and install build-essential and mtools.
sudo apt-get install build-essential mtools
If you are on a Linux machine you should also install qemu using
sudo apt-get install qemu
however if you are on a Windows machine you can download QEMU from their website or use this link.
Then you can go to gnu-efi directory and run make command.
To build the project you need to go gnu-efi directory and run
make bootloader
then in kernel directory you need to run
make kernel
and finally
make buildimg
after that you can start QEMU using
make run
if you are using Linux or you can run start.bat if you are using Windows.