LabJacks are USB/Ethernet/WiFi based measurement and automation devices which provide analog inputs/outputs, digital inputs/outputs, and more. A LabJack is an essential part of a computer-based instrumentation. If you want to make a computer-based system that acquires readings from various sensors/transducers, and controls various outputs/actuators, you need a LabJack to go between the computer and the various inputs and outputs.
Go to our main FAQ page for more basic questions like "What is DAQ (data acquisition)" and "What is an analog input".