Native Americans didn’t originally use or know about horses. They were introduced to them by the Spaniards!

Primitive horses lived in North America in prehistoric times. They died out during the last ice age. So, at the beginning of the Columbian Exchange, there weren’t any horses in North America. 

They were reintroduced to the continent during the time of the conquistadors, beginning with Columbus. He imported horses from Spain to the West Indies on his second voyage in 1493.

Then, domesticated horses were brought by Cortes in 1519. Mustangs were brought to Mexico and Florida. They were mostly of Arabian and Barb ancestry. Some of them escaped and were captured by Native Americans who quickly adapted to the horses and utilized them for transportation. They replaced the dog in carrying and pulling objects. 

Horses also improved battle strategies, hunting, and trade. Hunting bison was considerably improved by the use of horses who could keep up with the running herds. Native Americans grew more successful in hunting and using bison. 

(Source)