Load cells are used to measure weight. Load cells generally consist of a spring element on which strain gauges have been placed. The spring element is usually made of steel or aluminum which are very sturdy, but also minimally elastic. Load cell get slightly deformed under load, but then returns to its starting position, responding elastically to every load. These extremely small changes can be acquired with strain gauges. Then finally the deformation of the strain gauge is interpreted by analysis electronics to determine the weight.
Strain guage are electrical conductors firmly attached to a film in a meandering pattern. When this film is pulled, the conductors get longer. When it is contracted, it gets shorter. This causes the resistance in the electrical conductors to change. The resistance increases with strain and diminishes with contraction.
If an object is placed on the load cell or suspended from it, the object's weight can be determined. The intended load for a load cell is always aligned in the direction of the center of the earth, in other words in the direction of gravity.