Snakes comprise approximately 42% of all reptiles.
Snakes vary in many different ways (by looks, size, colors, husbandry, etc.), however due to constant human interaction the main concern of most people and the media are not the interesting lifestyle of the snakes, but instead the consequences of the snakes self defense mechanisms.
As far as the danger in snakes go, snakes are solitary creatures and will defend if necessary, and due to lack of limbs they may sometimes resort to biting as a Last resort. Most snakes are not venomous and are not deadly, some are moderately dangerous, and others can be lethal.
Some nonvenomous large snakes can be just as lethal or even more lethal to their prey compared to venomous species due to their powerful constrictions and therefore are not venomous as they do not require venom to survive.
Unlike other reptiles or amphibians where diet may vary in food groups, all snakes are carnivorous, some even eating other snakes.
There are about 2,800 species of snakes that are alive today, however you may not see most of them because they are usually minding their own business and taking care of us by making a meal of our pests ;)
Remember, the next time you see a snake (whether venomous or not), just leave it alone, and remember that it is very scared of you and just wants to get away and help us rid the world of disease and parasite infected rodents. Without snakes we could face another epidemic as serious as the bubonic plague.