flashing guide: 

(recovery roms)

- open twrp/ofox/pbrp recovery
- format /data
- flash rom:
   - install > select rom.xxx.zip
   - or adb sideload rom.xxx.zip (from a computer)
- reboot to recovery
- flash gapps (in case of vanilla rom):
   - same as flashing rom, see above
- flash fw (no need if already on latest fw):
   - same as flashing rom, see above
- reboot to system

(fastboot roms)

- reboot to bootloader {power + vol(-)}
- fastboot update —skip-reboot rom.xxx.zip
- fastboot reboot recovery
- format /data
- reboot to system