What is the work of macula??

The fovea is responsible for sharp acute vision (also called foveal vision), which is necessary in humans for reading, watching, and any activity where visual detail is of primary importance. The highest density of cones is in the fovea.

This link may help with other questions:   http://www.tedmontgomery.com/the_eye/macula.html

Why it is only one?? and why it is located near to blind spot.. Why not on any other place?

If they show clear images, why they are not more in numbers? so that we can see more clear images

The fovea is in the very center of the Macula. The macula is the avascular zone just temporal to the optic nerve head. Your question is similar to asking what the difference between a bulb and a headlight. The fovea is the tiny dimple in the center of the macula. when light hits it it has a white dot called the foveal light reflex. The fovea is responsible for your color vision and the fine details you can see. Only with a healthy fovea can you see 20/20.

(To confuse things even more, the small area just around the fovea is called the foveola)

The macula is still important for seeing color and detail but is mostly just an anatomical decription of the retina (like a bald spot). Macular degeneration affects the macula but is most debilitating when it disrupts the fovea.

The location where the optic nerve is bundled and leaves the retina is known as the optic disk. There are no photoreceptors at the location of the optic disk and hence there is a blind spot. The scientific term for a blind spot is a scotoma. So the blind spot due to the optic disk is a natural permanent scotoma in normal vision.