It will also explain what the difference between light duty and heavy-duty oils are and some comments about the special cases of synthetic and racing oil.
Some valuable information is already on the bottle.
On the front is the SAE viscosity grade, indicating the low temperature and high temperature viscosity of the oil. Back when engines had carburetors, how fast the starter could crank the engine determined if it would start at all. In time, another low temperature phenomena became important. The engine could still start and run, but the oil would not be sucked through the oil pump pickup tube nor slump into the oil pan. Sort of like trying to suck a milkshake through a straw.