If you're relatively new to the Mac, you may not fully appreciate that Finder is very tightly integrated to the rest of OS X. Finder is the application that allows you to browse your hard drive's contents (files, folders, etc). Finder, itself, has some pretty amazing power under the hood.
Spotlight is also an amazing technology that's built into OS X. It allows you to quickly and easily find any file on your Mac. Combining the power of Finder and Spotlight can yield some amazing results. Here's just one example.
Before I continue, let me provide a quick refresher on two technologies that we'll be talking about:
I think of Spotlight as Google for your personal computer. This is an app that you can use to search for anything on your drive. Want to find any document containing the word "computer"? Spotlight is your go-to app. Spotlight searches much more than just file name. It searches all of the file's content (even data contained within images). You can access Spotlight either by pressing Command+Spacebar or clicking on the magnifying glass in the top right corner of your screen.
Every file has metadata associated with it. Examples of this metadata would be date/time stamp of when the file was created, last modified, resolution (if the file is an image), etc. This is data generally more useful to the OS than to you, the user.
When you highlight a file or folder, you can get much more information about that file/folder than what you see on the surface by either pressing Command+I or by going to File > Get Info. In addition to the metadata related to that file, you can also use this utility to set access permissions for files, etc. Very useful stuff.
What I wanted to point out was the section near the bottom called "Comments".
This is an open-ended field where you can enter useful metadata about that file/folder. This is where it gets really cool.
Let's say you take a trip to Germany. While in Germany, you decide to take a tour of a Volkswagen factory and create a series of files related to that tour. Rather than searching on the term "Volkswagen" a year from now to relive those memories (which may return a LOT of files when you use Spotlight to search), it will be much more efficient to search for a term that you don't necessarily type very often, like "Fahrvergnügen". We'll select a related file, show Get Info and enter "Fahrvergnügen" in the "Comments" section.
Now, anytime you use Spotlight to search for "Fahrvergnügen", it will return a much smaller list (and more importantly, more accurate). You can use as many words as you want, and even words that make sense to no one but yourself. Feel free to be as creative as you want to be.