What is meaning of 18-55mm lens and what is ranger are available?

Answer 1

This a zoom lens (a lens whose focal length may be changed), and is of modest range. In early days of Photography, when 35mm film was first establishing itself as a virtual standard, a focal length of 50mm was considered to be that with a view comparable to that of the human eye.

For convenience, even though it is not true, lenses on digital cameras are often stated in measurements that are equivalent to the 35mm film numbers.

Perhaps we could have done better by expressing optical performance of the angle of the lens, which would be a constant number irrespective of the photo receptor size - but we didn't. For these numbers are dependent on the size of the optical recording surface.

Your second question regarding what is available - that depends on how deep your pocket is. Lens equivalents up to a several hundred mm's are commonly available. These almost always need a tripod to minimize vibration.

At the close-up end, 25mm is a common focal length, but much lower focal lengths start to become difficult. But available and pricey.