The Lens
The lens is the part of the camera that focuses all the little beams of light to a single point resulting in crisp and clear images.

Lens Markings
The lens usually has markings describing its focal length (in millimeters on point and shoot cameras and in meters on traditional lenses) and it's maximum apertures when zoomed in and out.

It may also give its ring size, meaning the size of the threading for putting on filters or extensions. Many point and shoot cameras have this threading up where the lens and body meet, though it requires an extension kit sold separately.

Focal Length
The easy way to think of focal length is how much you are zoomed in or out. That's not exactly the answer, but it's easier than "the distance from the nodal point to the focal plane" and way easier than the crazy math they show on wikipedia!

Field of View
Field of View is also known as Angle of View and describes the angular region of what is visually captured. That means how wide or narrow is the region you capture. Telephoto lenses yield a narrow field of view while Wide Angle lenses yield a wide field of view.

Crop Factor (Focal Length Multiplier)
Crop Factor is the term used to describe how lenses created for traditional negatives behave with a smaller sensor size. This is specific to cameras with interchangeable lenses only. The end result is that you get more telephoto than what the lens would indicate.

For example: A Canon Digital Rebel XTi camera with a traditional 50mm lens will have the same amount of telephoto as an 80mm lens on a 35mm film camera. The Rebel XTi has a focal length multiplier of 1.6X.


Digital vs. Optical Zoom

Digital Zoom
Digital zoom is a last resort setting. If you have it on, make sure you can tell when the camera has gone from optical zoom (the lens moving away from the sensor) to digital zoom (the camera using an algorithm to figure out how to make more pixels in a smaller area).

Basically this function is to allow you to take an image where you would otherwise not be able to, for example: from the stands at a rodeo, or from the wall at nascar. When you can't physically get any closer without putting yourself in harms way or breaking some law, then you use digital zoom.

Because it is more expensive to make a camera with more optical zoom, the more you get (3x, 4x, 5x, 6x, 10x) the more expensive the camera becomes, and usually the larger it gets.

Optical Zoom is the lens physically moving away from the sensor (the electronic noise and the moving lens).

Cleaning Your Lens
First, use something to blow off any abrasive dirt or sand. I use a Giotto Air Bulb which is cheap and just looks cool! Always use a micro filament cloth, not your T-shirt (Do as I say, not as I do). Put a small amount of cleaning solution on the cloth, not the lens or filter. If you put it on the lens, it inevitably leaves residue that attracts even more junk to your lens. Use small circular motion until the lens looks clean.

Changing Lenses
Because the sensor is blocked by your focal plane shutter, you can change your lens at any time without worry of damaging your images or sensor.

Push the button on the side of the lens and rotate it the appropriate direction (Nikon and Canon are opposite). Hold the camera lens side pointing at the ground to make sure dust doesn't fall into the camera. Put new lens on by matching the markings (red dot for traditional lenses, white square for digital only lenses) on the lens to the markings on the camera body and rotate the lens until it clicks securely.