A potentiometer is a manually adjustable, variable resistor with three terminals. Two terminals are connected to a resistive element, the third terminal is connected to an adjustable wiper. The position of the wiper determines the output voltage.

 

This small linear Potentiometer with plastic dust-cap is bread board suitable. this is center tap type so two outer pins will measure full 1K resistance and on third pin resistance will vary in accordance to rotation. small screw driver can be used for calibration of resistance value.