In the beginning, horses were wild animals. Horses were hunted for meat and especially for their hide (skin) which was used to make clothes, tools and tents.
It was not until around 3000BC that people began to tame horses. Although horses were still captured for meat, they were also tamed and domesticated so they could carry and pull things along. Around this time, the horses were too small to actually carry people. Eventually, they were bred to larger sizes and people were able to then ride horses.
It is unsure who tamed the first horses, it could possibly have been the indo-europeans, as horses were certainly evident when the indo-europeans arrived in Greece around 2100BC. However, one of the first horse images became apparent in the city of Troy around 1900BC with the famous Trojan Horse.
Even earlier than this, around 1200BC, in both China and Egypt, horses were being used to pull chariots. One particular ancient grave discovered in China, revealed 2 horses and a chariot rider buried together during the Shang Dynasty period. (The Shang Dynasty was a period of time when a large part of China was ruled under one king which lasted several hundred years – not with the same king of course!)
The taming of horses began to make life a little easier for people, particularly military men who rode into war on horseback or by having the horses pull war chariots, although this didn’t happen until the medieval times – before this era men would ride their horses to war, but dismount to fight. This changed in the Middle Ages when mounted knights were introduced.
With tamed horses, messengers could be sent quicker and you could carry food and tents on their backs making it easier to travel from village to village. 
People could carry goods for trading from city to city and farmers could have the horses pull carts of fruit, wheat and grain to the market places for selling. However, horses were not used to plough fields at this time, oxen were used instead. This was because horses were expensive and needed more quality food than oxen.
By the late fourteenth century horses varied in quality from an old nag worth 2 shilling to a noble mount costing 50 pounds or more. By this time an even greater range of horses were available. Horses were used for war and hunting and were a vital form of transport. From the 1560’s they pulled private coaches.
Agriculture (farming) and industry found horses indispensable for preparing the ground for crops, operating various pieces of machinery and pulling carts and wagons.
Horse racing began in the seventeenth century under royal patronage and provided for scope for different breeds. The strength, speed and courage of the horse reflected the owners status in society.
The eighteenth and nineteenth centuries saw the introduction of horse racing, country sports and hunting with dogs which was leisure for the aristocrats of society. The upkeep of horses became more important than upkeep their servants for the rich people. A man would pay a horse painter 50 pounds to paint a portrait of his horse, but think it too much to pay 10 pounds for a portrait of his wife. 
Hunting, sports and fishing still remain regular sports for aristocrats, however, horse racing now appeals to the masses. Horse riding in general has become a leisure interest instead of being depended upon as transport, thanks to the invention of the combustion engine which is used in cars and other vehicles.