There are many theroies as to why crystals do what they do. To break it down to the very basics: Vibrations. Although it appears that it is only us living organisms that appear to be moving in an otherwise very still inanimate world, this couldn't be farther from the truth. When broken down into the most basic building blocks of molecules and atoms, everything is in motion. Everything vibrates. As humans, we enjoy things that are familiar and compatible to us. We like our group of friends, we like "our" spot on the couch, we like the smell of our mothers home cooked meals. Energetically then, we like things that vibrate at the same frequenceies as us. The molecular structures of crystals vary widely, and their uses even wider. So wide in fact that they are used in the technology we use daily. Our cell phone batteries, radio recievers, and so much more. Science is just starting to catch on to the energetic properties of these crystals that the ancients have known for thousands of years.
Today, you and I can utilize raw crystals to improve our everyday lives. Through years of intuitive research many crystal experts have agreed on the energetic properties and uses of crystals. With this knowlege we can narrow our searches for the right crystals for us faster, by understanding what we need and what they offer. It is always best to pick out your crystals in person, so you can hold them, interact with them, and feel them before purchasing them. We are attracted to crystals that vibrate at the same frequencies as us. Want to work on another area of your life but aren't quite to that vibration yet? You can pick crystals with the properties you desire to attain and work with them to raise your vibrations to that level.
Working with your crystals
Now you have your crystals, great, but what comes next? It can be as simple as carrying the crystal in your pocket every day, or as complex as creating crystal grids with lots of crystals and meditating with them. The point of crystals however, is to be consiously aware of them. While they look beautiful sitting on your dresser, if it isn't there when you need it how can the crystal do you any good? By keeping them in your pocket, or as a peice of jewlery you can take them out any time and fidget with them as needed. If you believe nothing else, at least it can be a placebo reminder of the attributes to which you are trying to attain.
Cleansing your crystals
Just like batteries, crystals need to recharge. You can do this by placing them in sunlight, moonlight, or putting them under running water. Lots of crystals have protective properties that soak up the negative energy so you don't have to. Once they fill up on negative energy they stop taking it in, and no longer work. You must periodically cleanse crystals of the energy they soak up; by either a sunlight or moonlight, water, or a salt bath. Being of the earth you can also bury them in soil for a while. Just remember where you put them! Each crystal has a preffered method of cleansing. Stones of the Solar Plexus chakra, which is associated with the sun and light, prefers to be cleansed in the sun. Stones associated with the Root Chakra will prefer to be burried in soil, salt, or salt water.