The blinking mechanism in humans as well as many other species can be likened in a way to being the same as a car windscreen wiper. The premise being that during the course of the day tiny particles of dust and pollen to name two, as well as many other substances will float onto the surface of the eye which can cause irritation, infection of can just plain get in they way when they build up. And as well as these tiny particles we also have larger objects blown onto the surface of the eye that we can feel, and will often try to remove manually (with our finger). The eyelashes in this respect work like a brush to sweep particles off of the surface of the eye, enabling us to continue see properly.
As well as this there is also a secondary use for the blinking mechanism as well. That being to, through the movement of the eyelid over the surface of the eye, to spread tears across the surface of the eye, which are antiseptic, helping prevent infections, and of course keep the eye from drying out. In humans blinking and winking are also uses of body language and social interactions respectively, although these of course have developed independently to the evolutionary usage of blinking. In general we will blink between once every two and ten seconds, such is the need for removing debris from the eye surface, although this figure can be increases in certain environments where there is more debris than normal, such as in a high wind or in a very dusty environment.
Humans are also one of the only animals that can control their blinking and can force themselves to blink or wink whenever they want to. Most other special of animals that do blink do so subconsciously and have no control over when they do it. Humans do blink in this way as well of course and do so with both eyes at the same time, where some other animals, rabbits for example will blink each eye independently of the other.