Names given to the Spanish language
Formally speaking, the national language of Spain, the official Spanish language, is the Castilian language (as opposed to regional Spanish languages like Galician, Catalan, Asturleonese and Basque). As such both names, "español" and "castellano", have distinct and independent meanings that may be required for clarity in some specific contexts.
Generally speaking, though, both terms can be used to refer to the (national) Spanish language as a whole, with a preference for one over the other that depends on the context or the speaker's origin. "Castellano" (as well as "Castilian" in English) has another, more restricted, meaning, relating either to the old Romance language spoken in the Kingdom of Castile in the Middle Ages, predecessor of the modern Spanish language, or to the variety of Spanish nowadays spoken in the historical region of Castile, in central Spain.
Andalusia
Andalusian Spanish is one of the most widely spoken forms of Spanish in Spain, and because of emigration patterns was very influential on Latin American Spanish. Rather than a single dialect, it is really a range of dialects sharing some common features; among these is the retention of more Arabic words than elsewhere in Spain, as well as some phonological differences compared with Standard Spanish. The isoglosses that mark the borders of Andalusian Spanish overlap to form a network of divergent boundaries, so there is no clear border for the linguistic region.