Taimur Khan

I am a begginer and read somewhere that you need to drive on High most of the time and switch to Low only if you have a refusal. ( I am presuming Low means 4x4 ). Does Low mean 4x4? ( I have a Prado ). So should he have changed to 4Low before negotiating the dune? Pardon me if it's a stupid question. But am just learning.