Reptiles are are cold blooded, or incapable of generating their own heat!
To stay alive, they must take in heat from their environment, and so must live in a habitat that provides both warmth and protection. These animals are often seen sunning themselves on the rocks or river banks of their habitat.
The term "reptile" covers a wide range of different species and animals.
Snakes and lizards fall under this umbrella, as do turtles, tortoises, crocodiles and alligators. Some specialized animals like the giant tortoises and dragons of the Galapagos Islands are reptiles as well, and adhere to the same basic characteristics as more common American lizards and tortoises.