2000 Toyota Yaris recharging battery using booster pack

Electrical problem
2000 Toyota Yaris 4 cyl All Wheel Drive Manual

was wondering what the following means on the booster pack instructions - attach the red cable to the positive on the battery - this I understand - BUT what does it mean when they say attach the black to an EARTH POINT on the engine - attach it to a non-moving metal part on the engine.I'm a bit confused. Or can I attach it to the negative on the battery? However, my Yaris manual says that when recharging the battery whilst still in the car, the GROUND CABLE has to be disconnected.I'm a bit confused, - DO I disconnect the negative on the Toyota battery as instructed in manual - then attach the red charger cable to the positive/red on toyota battery, and do I then attach the recharger cable on an EARTH POINT or on the NEGATIVE POINT ON THE YARIS BATTERY which I would have disconnected (the booster says not to attach the black cable to the negative side of battery, but do I still disconnect this cable on the Yaris battery? - Car is a Toyota Yaris - i've had it for about three years but maybe the car is only 5 to 6 years old