Snakes belong to the Serpentes category. There are small species, like the 87 odd species of thread snakes, and there are gigantic ones, like the anacondas and reticulated pythons. Contrary to the popular belief, not all snakes are venomous. Similarly, some are terrestrial, while others are aquatic.
Note: People do keep snakes as pets, but then one has to be a little careful whilst choosing the species. It's not just about your safety, but also about the safety of the snake.
In terms of appearance, they are almost similar to lizards, which explains why they were originally classified as lizards in 1831.
Next time you see any of these species, do not be afraid. They are just misunderstood creatures. If you see them closely, you will find that just like cats and dogs, even they can be very cute and adorable.