Reboot your phone to bootloader: adb reboot bootloader
fastboot devices
Checks fastboot connection.
fastboot oem unlock
Unlocks the bootloader (varies by manufacturer; on Pixels it's fastboot flashing unlock).
fastboot flash recovery twrp.img
Flashes a custom recovery image.
fastboot reboot
Restarts the device normally.
Once your command window is open, here are the most common commands you will use with v1.4.3:
1. Check Device Connection:
adb devices
2. Reboot to Bootloader/Fastboot Mode:
adb reboot bootloader
3. Check Fastboot Connection:
fastboot devices
4. Flash a Recovery Image:
fastboot flash recovery filename.img
Given that Google releases Platform Tools monthly, why stick with a 7+ year old portable tool?