Spain is a "parliamentary monarchy" : art. 1.3 of the Constitution (1978)
The King is the head of state, but with a role largely restricted to the ceremonial : articles 56 to 65 of the Constitution.
The national executive is headed by the Presidente - usually the leader of the largest party or coalition in the National Assembly.
The President appoints the members of the Consejo de Ministros.
The Consejo del Estado advises the government.
The national legislature is the bicameral Cortes Generales (National Assembly): Congreso de los Diputados and the Senado.
Proposed legislation is introduced inot the Congreso de los Diputados (Lower House), the Senado having powers of veto or amemdment.
Once the legislation has been passed by the Cortes Generales, the King must "sanction and promulgate" it: art. 62(a) Constitution.
Spain is part of the civil legal tradition.
The Spanish Constitution (English, Spanish) is the primary source of law. The Tribunal constitucional interprets the Constitution, ensures that the exercise of power by both the legislature and the executive is constitutional, and protects the rights of individuals. The decisions of the Tribunal are published in the BoE.
The Spanish judiciary is governed by the Consejo General del Poder Judicial. It has 21 members, who are chosen by members of both Chambers of Parliament -- the Congreso de los diputados and the Senado -- in equal numbers. The members then choose their president, who is also president of the Supreme Court -- the Tribunal supremo.
The Spanish legal system is defined by the Ley Orgánica 6/1985.
Spain's Supreme Court. It is divided into five chambers: civil, criminal, administrative, social and military.
The National Court. Has jurisdiction in the following areas: de lo penal (criminal), de apelación (appeal), de lo contencioso (administrative), de lo social (labour).
Autonomous communities have executive and legislative powers but not judicial power, so the tribunales superiores de justicia are technically courts of the state. They have jurisdiction over the civil, criminal, administrative and social matters in the territory of the autonomous community where they operate.