Gravitational field strength, g, tells you how strong gravity is in a place. It is the weight of each kilogram of mass, measured in newtons per kilogram (N/kg). On Earth g is about 10 N/kg, so every kilogram weighs 10 N. On the Moon g is about 1.6 N/kg, so every kilogram weighs only 1.6 N.
From W = m × g, for a fixed mass the weight is directly proportional to the gravitational field strength. A stronger field gives a larger weight, and a weaker field gives a smaller weight. A graph of weight against mass is a straight line through the origin, and its gradient is g.
A 10 kg object weighs 10 × 10 = 100 N on Earth but 10 × 1.6 = 16 N on the Moon. Its mass is 10 kg in both places, because mass does not depend on gravity. Far from any planet or star, the gravitational field strength is close to zero, so the weight of the object is almost zero while its mass is unchanged.