The use of 144Hz is the refresh rate at which your monitor will receive the signal from your GPU. With this frequency you can get better response times and reduced input lag, ideal for FPS games if you are very competitive. To achieve the effect, you will need to tune down your graphics settings until you start getting more than 144 frames per second.
P.S. I forgot to mention, you will also need a Display Port cable for this to work.
Cheers.