Have you ever taken a picture and processed it on your computer, then gone to have it printed out and gotten a print that looks different from what you saw on your monitor? If so then you likely need to have your monitor calibrated.
The disconnect comes because monitors and printers read and display color differently, so it is sometimes (most of the time really) necessary to need your monitor to be calibrated so that the colors you see on your screen match what a printer can recreate. So, if you have any intention of having your images printed after processing them on your computer than you should really think about having your monitor calibrated.
There are many products out there on the market to calibrate your monitor, I personally use a Sypder4 system by Datacolor. Mark Wallace from AdoramaTV recently did a great video working with an Xrite system called i1. He also goes over why you need to calibrate your monitor and the differences between prints and your monitor. Take a look below: