This is a simple overview of the k-NN process. Perhaps the most challenging step is finding a k that's "just right". The square root of n can put you in the ballpark, but ideally you should use a training set (i.e. a nicely categorized set) to find a "k" that works for your data. Remove a few categorized data points and make them "unknowns", testing a few values for k to see what works.