A camera lens (also known as a photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically. We have a wide lens for clicking wide-angle pictures whereas we also can get a macro lens to click close-ups of different objects.
There is no major difference in principle between a lens used for a still camera, a video camera, a telescope, a microscope, or other apparatus, but the details of design and construction are different. The focal length of a lens is calculated in mm, a higher number in mm of a lens means that it can zoom more. The lower number means that it can take wide-angle shots which would not be possible on other lenses. On a higher number of lenses, higher than 50mm means that the focus will be on a smaller aspect of the view.
While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these and produce a design that is suitable for photographic use and possibly mass production.