1、Download the ROM and put it on sdcard. Root isn‘t included in ROM yet. You can grab the lineage addon here (removal addon here). If you want GAPPS too, then download MindTheGapps (mirror or Open Gapps too (choose arm64, 8.1 and pico or other variant if you want more gapps).
2、Reboot in TWRP by pressing all 3 buttons (Volume UP + Volume Down + Power).
3、Wipe system, data, cache and dalvik-cache. Flash the ROM from the directory where you‘ve placed it.
4、Flash lineage‘s root addon / GAPPS (OPTIONALLY).
5、Reboot.
