If you want to download and flash custom ROMs on to your Moto G Turbo from Motorola, you will need to flash something called TWRP. The TWRP is apparently that will open doors for custom firmwares and all sorts of hacks that were not allowed previously.
Download Moto G Turbo TWRP custom recovery
In order to get TWRP on your Moto G Turbo, you will need ADB on your windows computer. ADB allows your phone to communicate with your PC. Use this command to flash it,
fastboot flash recovery twrp.img
Keep in mind that in order to flash TWRP onto your Moto G Turbo, you will need to unlock the bootloader. Visit motorola’s website about it.
That is it, you will have successfully flashed TWRP onto your Moto G Turbo. As a habit, you should always do a full backup of your phone before messing with the recovery or firmware that came on your device.