Strain gauges are resisitve sensors whose resisitance is a function of applied strain (unit defermation). Stress is calculated from the strain information.
Typically a strain gauge is attached to a structure and when such a structure is deformed (tension, compression, shear), the resistive strands in the strain gauge follow the structure deformation which causes an electrical resistance change. the resistance change is then expressed in units of stress or strain.
VPG Bondable terminals
For many types of strain gauges instrument leadwires generally should not be attached directly to the solder tabs of the gauge. Instead the normal practice is to install bondable terminals adjacent to the gauge and connect using small flexible jumper wires.
Bondable terminals details and description details here
VPG Strain gauge instrumentation
Data acquisition instrumentation is used to sample real world physical conditions and conversion of the resulting samples into digital numeric values that can be manipulated by a computer. The components of data acquisition systems include sensors that convert parameters to electrical signals, signal conditioning circuitry to convert analog waveforms into digital values for processing, and software programs using various general purpose programming languages.