Very simple. The zip includes two .ini files to put in "/bootloader/ini/".
They let you boot the payload from the hekate menu so you can choose to autoboot the CFW of your choice directly from hekate.
You have to put fusee-primary.bin or ReiNX.bin to "/bootloader/payloads".
This is useful for people that wants to use the hekate bootloader (or uses injector dongles) but also wants to autoboot to the desired CFW.
To set the autoboot in hekate go to "Options > Auto boot > More configs... > Fusee Primary/ReiNX"