The Spanish language is a latinate idiom which originated in the Iberian peninsula, initially in the northern regions close to the Basque countries, and which was spread afterwards to encompass all the peninsula (except for the region where Portugal was established). Spanish belongs to the Ibero-Romance subgroup of Latinate languages.
After Christopher Columbus sailed to the west and discovered the new world (or american continent), the spanish language was spread to those new lands. Today it is the language which is spoken by most people in the Americas, with more than 360 million native speakers.
Spanish is commonly taught as second language in the United States, due to the historical connections between the colony of New Spain (Mexico) and the southwestern states (California, Arizona, New Mexico, Texas), which were part of the spanish colony before the USA annexed those territories after the Mexican-American war.