The theory of evolution dates back to the 1800's when Charles Darwin was around. Darwin went to different islands in the Galapagos and he found something very strange; although he found the same birds everywhere, they each had different beaks depending on what they ate. This can be seen in other animals as well. All animals have evolved over time and this can be seen clearly. For example, a stoat in summer has a brown fur coat, whereas the same stoat in winter will have a white coat. These coat colour changes help the stoat hide from predators and hide from prey.

Certain genes together are called genotypes. 
How an animal/ individual looks as a result of their genes is called a phenotype.
All living things are classified using the dichotomous tree and are then put in their respective kingdom, phylum class etc... here is a video to help you remember it.