Help to understand iPXE

[Itay1787]

Hi, I'm new here,
I would be happy to help and guidance
I currently use Fog for some of my stuff but the netbootxyz idea is cool
And I want to add fog to the main menu of netbootxyz and have no idea where to start...
This means that I want the main menu to have the efi file of fog and then it will switch to fog because I cannot use more than one PXE Server via DHCP...
I tried to understand how at first it recognizes what is considered local in order to mount the HDD and its timer but I could not understand how it knows that this is the default one... and how the timer is set to one file but the HDD set one a different file and I can't find a variable or something like that.
I'm new to all ipxe files and if you can help or even give me guidance/guides, I'd be happy!