Default Quick Rundown

Ok, been away from the note 2 for a min. Anyone want to give me the low down on all this 4.3 stuff? I'm seeing roms say that MJ9 has to be flashed in Odin before a the rom can be flashed? Is this a one time deal or does it have to be done every time I want to flash a tw rom? Do I have to do anything to go back to an aosp rom? I'm sure I could figure all this out on my own but I'm impatient. Lol. TIA

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