TWRP backups these things by default:
-
boot
partition. This contains the Linux kernel executable (important) and some other data to boot the device. -
system
partition. The/system
“folder” in Android contains the operating system without changes. That includes all the UI, system apps and how the system works, in general. -
data
partition. The/data
“folder” in Android contains your system settings (wifi points, preferences, contacts, etc), those apps you have instaled, and the app data for your apps and system apps (chat conversations, notes, e-mails, app preferences, your favourite game’s records, etc).
TWRP saves each partition in a raw dump (a file you cannot open normally). The NANDroid backup (as we call the collection of raw dumps) is saved in the TWRP/BACKUPS/<device_code>
folder in the FP2 internal storage (formerly called sdcard
as in your linked article, but /storage/emulated/0/
for newer Android versions).
Because of that, TWRP doesn’t backup user data (internal storage, or /storage/emulated/0
) because that will be recursive (saving internal storage in internal storage). You should transfer those contents to your computer with an USB cable via Android’s MTP (TWRP also has a built-in MTP, easier in my opinion).