I like to explain this by using dogs as an example.
All dogs have fur, legs, tails, eyes etc. but you also have different breeds of dog, with all of the previously listed things but slight changes such as some having long fur, and others short, for example.
So, if you have a class called
dog, the class called
jack_russell_terrier would inherit the properties of
dog, but would have the extra features that make a jack russel terrier different to other dogs.