Reptiles make a natural group, because they all have scales and similar internal anatomy. They vary in their methods of reproduction, and are divided by this.
Lizards mostly have legs, though some have lost them. Snakes have no legs, but evolved from reptiles with legs, as can be seen in the fossil record.
Snakes are a natural part of the environment, and play a part in maintaining normal natural balances. They should be preserved, like all the other parts.
Most people who are bitten by a snake are bitten while trying to catch or kill a snake that could just as easily have been left alone. There is a lesson here.
Tuatarans are primitive reptiles which only managed to survive in a few isolated parts of New Zealand, where they were able to avoid predators and competitors.
Turtles and tortoises are reptiles that have shells. Turtles need to come ashore to lay their eggs, which leaves them and their young at risk from predators.
Dinosaurs are one of the groups of extinct reptiles, and based on their skeletons, they may be further divided into lizard-hipped and bird-hipped forms.
Extinct reptiles can be reconstructed from fossil evidence, but reconstructions are often coloured by people's assumptions about how the animals behaved.
Dinosaurs lived for a long time, a long time ago, and probably died out (as dinosaurs) as a result of an asteroid strike that changed the climate.
Dinosaurs are usually referred to as having died out, but there is a lot of evidence to suggest that the birds are just modern warm-blooded dinosaurs.
There are some scientists who would happily treat the birds as part of the reptiles group, while others would include the monotremes as reptiles.
There are many theories about how the dinosaurs died, and we will probably never know what really happened, but the asteroid theory looks good.
There were other ancient reptiles around at the time of the dinosaurs that were not dinosaurs, and some of them survive today, like crocodilians and tuatarans.
The first people to make the ancient reptiles well known were Caspar Wistar, Mary Anning and Gideon Mantell. Richard Owen also helped.
Even now, we only have a very partial picture of the dinosaurs, because the fossil record is far from complete, but every year, new founds are made.