Android

https://opengapps.org/

https://twrp.me

https://lineageos.org/

Fastboot:

On your device, go into Settings → About and find the Build Number and tap on it 7 times to enable developer settings. Press back and go into Developer Options and enable USB debugging. From your computer, open a command prompt and type:

fastboot oem device-info
fastboot devices

to check, if device is recognized.

To flash TWRP: Download the to your phone matching image file on https://twrp.me/Devices/ and copy the file into the same folder as your adb and fastboot binaries. Rename the image to recovery.img and type:

fastboot flash recovery recovery.img
fastboot boot recovery.img

You should now be in TWRP Mode.

Just reboot:

fastboot reboot

Useful commands:

fastboot flashing unlock
fastboot oem device-info

ADB:

adb devices
adb logcat
adb shell
adb reboot bootloader

You should now be in fastboot mode.

Problems? Check FW and adb driver!

Flash:

Dalvik/ ART Cache
System
Data
Cache