Question: 5V independant power suppy, UART3 and UART4

[BobCraig10]

I am sorry to ask this here, but I did not know where else to ask, or how to tag it as a question not an issue. I am trying to find out about the ports on the back of the screen, also the filament runout port. I'm just trying to learn. The 5V dc port, is that to power the screen, or to power an external device? If it is for an external device, what is the power rating? For the Filament Runout detection port, Does this port have the same address as the mainboard the screen is plugged in to? How do I address this port/pin in Marlin? The UART connections, what would they be used for? Would they be used to connect a raspberry pi for octoprint, or maybe an esp8266 to control say, external lights, or fans controlled by situations pertaining to the printer status or commands? Thank you in advance for any help, and persevering with my questions, like I stated, I am just trying to learn. If there is a better place to ask questions like this, please let me know, and thank you all for the help you have already been in the past.