Generally, when you purchase a camera these days, it will have some sort of lens attached. To offer some versatility, it will more than likely be a zoom lens, with an average range in the vicinity of 17mm to 200mm.
In the old days, well before digital came along, cameras generally came fitted with a fixed 50mm “standard” lens. It was called that because the picture it produced had much the same perspective as to how the human eye would perceive that same scene.
However, There were many thousands of great private, commercial and historical records made with this little lens, but today it is considered uninteresting to say the least, compared to some of the modern and versatile zooms now available on the market.
So, the 50mm became known as the “standard” lens (excellent for wide landscape vistas) and anything below that became the “wide angle” lens, on down to the “fish eye” at around 15mm, which will give an extra wide angle of view of around 180 degrees.
These extra wide angle lenses are very expensive and will probably only get used on the very odd occasion, because of the way-out looking perspective they can have on subjects and especially facial features.
On the other end of the scale, there are the “narrow” angle lenses. These are known as “telephotos” and they enable you to get closer to your subject without having to alter your position. They can range from 200mm to 800mm and beyond and are also very expensive. The ideal lens for portrait work is one that has a focal length of about 135mm. Also known as the “people” lens.
Then there is the Macro lens for close-up work, but that’s another chapter.
So far we have been talking about “fixed” or “prime” lenses. That means that they are of only one focal length. They do not zoom.
The focal length of a lens can be defined as the distance from a point within the lens to the film plane or digital sensor, when the lens is focused on infinity. Focal lengths are normally found on the lens barrel and stated in millimetres.
Your camera was probably fitted with a zoom lens, as they usually are these days. Also available are wide angle zooms and telephoto zooms.
The term “fast Lens” relates to the actual size of the maximum opening of the diaphragm or aperture of the lens and allowing the maximum amount of light to enter the lens. And the more light that enters your lens the faster the allowable shutter speed and that is where the term derived from.
So your zoom lens might have a maximum aperture of f5.6, but a fixed 50mm lens could have a much wider aperture of f1.4.
Remembering of course, larger number - smaller aperture.
And you should also remember, for a f1.4 lens you will pay 3 or 4 times as much than you would for a f5.6 lens.
But apart from a little bit of light loss, with the quality of zoom lenses being manufactured today and through the magic of photo editing programs, it takes a very keen professional eye to find any difference.