Ok, here is a comprehensive steps to install the twrp and rom on your device.
TWRP FLASHING & ROM INSTALLATION
1, Put device in fastboot mode (vol- and power button. Release power button after device restarts. Release vol- after you see fastboot screen)
2, connect device to PC
3, from adb folder type "fastboot flash recovery twrp.img" hit enter
4, after flashing is complete, type "fastboot reboot recovery" hit enter (device will reboot to twrp).
If you will like to backup your internal storage, see section
"BACKUP INTERNAL STORAGE" if not, proceed to step 5
5, in twrp, go to "wipe > format data" type "yes" hit enter
(ALL DATA ON YOUR DEVICE WILL BE WIPED, MAKE SURE YOU HAVE A BACKUP OF YOUR INTERNAL STORAGE)
6, reboot to twrp (twrp main menu > reboot > recovery)
7, in twrp main menu Go to “Mount“.
8, tap on “Enable MTP” option at the bottom right. (after that, the device will be recognized on your PC.)
9, transfer ROM zip to your device storage
10, install rom
11, wipe cache and dalvik
12, Reboot system.
Done !!
First boot will take some time, so please be patient
BACKUP INTERNAL STORAGE
1, in twrp go to “Mount“.
2, tap on “Enable MTP” option at the bottom right. (after that, the device will be recognized on your PC.)
3, copy your files from internal storage to your PC.
4, when you are done, proceed to step 5 in section
"TWRP FLASHING & ROM INSTALLATION"
NOTE
if asked for a password in twrp, enter you device lockscreen password.
hope it all works out well for you
Cheers!