How to add ota function

[Karrthik23]

I am trying to update my code via OTA and i was confused about how to go about that
firstly
when i try the serial upload i have 4 bin files (bootloader, partitions, main code etc)
when i am trying to do ota which bin file should i be uploading( i am guessing only the main code bin)
in the code provided, once the data packet is recieved, addresses have been defined like (pData[0] == 0xFB)
what does 0xFB stand for(like corrposponding to which address)
other addresses given are
0xFC
0xFD
0xFE
if i could get some clarity on that i would be really greatful as i am new to iot and ble implementaitons