Hello there,
Argon, ArgonNX, ArgonNX-SE, fusee and Hekate all of them are bootloaders
Argon(NX-SE) is a chainloader, a bootloader designed to bootload any other payload, the main purpose or Argon is to avoid the need of update the payload of your injector.
On the V1 switch you can use an external or internal device to inject the payload and sometimes is a pain on the buttocks to update the device's payload and you must do it each time your bootloader get updated
On V2 Switch you install a modchip which loads the SDMC:/payload.bin file so you need to upgrade that file each time your bootloader get updated.
The preferred bootloader is Hekate, and most people setup Hekate to autoboot a configuration. other people prefer hekate GUI (NYX) to load and there select the config to boot.
Here is where Argon(*) born, Argon replace your first step of bootloader so you have not to upgrade the payload. Argon chainload any other bootloader you like, by example, hekate so you only upgrade the needed files and forgot about your injector.
The most common setup is:
Your injector (external, internal or modchip) loads Argon, then you setup Argon to auto chain-load Hekate.bin. then hekate loads your configuration or NYX if you like.