The horse, zebras and asses all belong to the family of mammals called Equidae. They have only one hoof on each foot, compared to the cow which has two. Their nearest evolutionary relatives are the rhinoceroses and tapirs.
All Equids feed on grasses and shrubs found in the open country and rely upon being swift runners to flee from predators. They have a highly developed social structure and live in family groups which join together to form herds.
All the variations of modern domestic horse from the smallest Shetland pony to the largest Shire belong to the same species - Equus caballus.
It is useful to know the names of different parts, colouring and markings of the horse as they might be referred to in lessons. There are many books available which go into much more detail but this section of pages might help as a start...
Many descriptive terms and names can seem arcane today but have been handed down from the long history of association between man and horse.
Next - the importance of the front and back.