The Digital images are made of millions of tiny tiles-like elements. The more these tiny elements (called pixels), the more will be the resolution. A single mega pixel is equivalent to one million pixels in an image.
If you know width and height of an image you can calculate how many pixels your camera gets (by simply multiply them). Also, the megapixels have nothing to do with the quality of image. Quality depends on exposure, focus, lighting, camera lens etc.
However, the human eye doesn’t work like a digital camera. In good light, you can distinguish two lines if they are separated by at least 0.6 arc minutes that means equivalent pixel size is 0.3 arc minutes. Now take 120 degree horizontal field and 60 degree vertical plane as your total plane of view. Then resolution of your eye would be:
120 * 120 * 60 * 60 / (0.3 * 0.3) = 576000000 pixels = 576 Megapixels