How did the Lakota use a coup stick?

First I would like to note that the Sioux were not the only tribe to use the Coup Stick.

Also note that the concept has been perverted by European settlers.

"Counting Coup" was a method of battle used by many of the horse tribes. It consisted of using the stick to tap or touch an opponent during battle. To prove a concept, of : "I could have killed you but chose not to" (as a basic example). Rank was assigned by the danger involved in each act.

European settlers would often attack after this was done, and this is dishonorable and often resulted in an all out attack against the settlers.