For historical reasons, variable resistors are often called 'pots' which is short for 'potentiometers'.
In our experiment with the Serial Monitor, the pot is somehow varying the voltage at A0 and the little test sketch is converting this voltage into a number between 0 and 1023.
Your pot has a circular 'track' that acts as a resistor, in our case it's a 10 kΩ resistor. However, the difference with a pot, is that there is also a middle connection called the 'slider'. This connection is rotated when you turn the pot. So if you connect one end of the pot to 5V and the other to GND, then the voltage at the slider will vary between 0 and 5V as you turn it.