Instructions
Click on the research bar at the top of the screen to open the technology tree window.
Select "Agriculture" to learn this technology. Based on various factors, such as the amount of people in your town, it can take anywhere from 5 to 20 turns to learn. Continue to play the game as normal until the required amount of turns have passed.
Open the technology tree and select "Animal Husbandry." Once this technology has finished, all available animals are shown on your map. Due to the random nature of "Civilization IV," horses appear in a random spot each game.
Build a new city next to the horses if they are out of the range of your current cities.
Select a worker. Click on the horses and select "Pasture" to have your worker build a pasture on top of the horses.
Connect the pasture to your city with roads once the pasture has been built. This supplies the nearest town with horses.
Connect all of your cities together with roads to supply horses to your entire civilization, opening up new units and technologies such as horseback archers.