[Galaxy Note 4 Q&A, Help & Troubleshooting] dork997:
Rom has 5 parts, 1) main android os 2)Modem: it controls radios of your phone 3)bootloader: it supports booting up the phone, flashing *official* firmware , it will decide if a upgrade/downgrade is compatible basically works like BIOS but note that it will let you install only official versions of android signed by samsung, samsung official firmwares can be downloaded from website called sammobile, after you have downloaded a firmware in your pc it will be in the form of zip file, when you extract that file you will get a file in the form of .tar.md5 format if this file is extracted again then it will split up in parts like bootloader, recovery etc but you don't need to extract it again just flash the .tar.md5 file to Flash samsungs official firmware in order to do this you will have to enter bootloader's download mode on your phone this is done by turning off the phone then pressing volume down+power button+homekey on your phone the phone will boot into download mode will ask you to confirm firmware installation by pressing volume up key, *BUT* remember the downloaded firmware file is still in your pc so now to transfer and install it in your phone you will need a Pc software called "odin" just google "odin xda" and you will find download links, after installing and opening odin you will see it has 4 options BL, AP, CP,CSC (these are the rom parts i told you about you click BL and it will ask you to locate the bootloader you want to flash on your phone, click CSC it will ask you to locate the csc file you want to flash) but since we did not further extract our downloaded firmware we don't need to locate and flash these different parts manually if we just click "AP" and locate the downloaded .tar.md5 file it will automatically flash the whole firmware along with its bl,csc,cp and ap NOTE: First you have to put your phone in download mode then you have to connect it to your pc via cable and open Odin it will intimate you with a green box saying "connected " then you can go ahead and flash ur firmware 4)csc: this is country specific code, it enables/disables functions in the phone for eg the Samsung android firmware released in uk will hve its own csc and minor functions...and a firmware released in france will have its own csc and minor differences. 5) Recovery, this lets you clear cache, do factory reset etc in most samsung phones recovery can be accessed by shutting down phone and then pressing volume up+power button+home button at the same time and phone will boot into recovery mode. There is just an overview on how to flash different versions of "official samsung" firmwares on your phone before learning how to flash custom firmwares i suggest you learn how to flash stock firmwares first ( incase the custom os messes something up in your phone you will be able to get back to official software) There are many videos on youtube demonstrating how to flash official firmware via odin first watch a few videos on youtube before performing this.

NEXT: CUSTOM OS

Custom Roms like (stock android rom which is known as "cm" ) can not be flashed via Download mode which i talked about earlier in order to flash a custom rom you will need a custom recovery the official samsung recovery was limited to clearing caches, doing factory reset etc but these custom recoveries like TWRP, CWM have additional functionality which lets you flash custom roms (without entering and going through download mode) so in order to flash a custom rom you will have to download the custom recovery (i recommend twrp) for your phone's model from twrp.me (be careful install the one which is specific to your model or you could brick your phone) just download the recovery file in your pc, when you go to downloads section of twrp it will ask you to choose the format in which u want to download the recovery just download the one ending with .tar . Now to install this custom recovery in your phone, put your phone in download mode and connect with your pc and open odin, select "AP" option and locate the downloaded .tar recovery file and flash it. Now when you have flashed this recovery if you go to recovery mode (VOLUME UP + POWER + MENU while phone is off) you will see a different recovery than samsung's stock recovery.....this one will have many additional functions and options . At this point don't do anything just reboot your phone. Now that we have a custom recovery we can go ahead with downloading and flashing a custom rom to install a custom ROM follow the below instructions

> download the custom os u want to install (CM in your case) and place it in your phone's sd card, boot into recovery mode choose the option "install" it will ask you to locate the file, select the downloaded rom file and it will flash it. TADA...you will now have the custom rom running on your phone NOTE : again this is just an overview i suggest you watch videos on youtube and do alot more reading before doing this.