The single most useful thing to know about eating in Spain is that the meal times are different from most other countries, and that trying to eat on your home schedule will result in either empty restaurants or tourist traps. The Spanish eat lunch between 2pm and 4pm, and dinner between 9pm and 11pm. Restaurants that are open at 7pm are open for tourists, not for locals.
The Menú del Día
The menú del día is one of the great institutions of Spanish eating. Available at lunchtime in most restaurants, it typically consists of a first course, a second course, bread, a drink, and dessert or coffee, for a fixed price that ranges from about €10 in smaller towns to €15–20 in major cities. It is almost always better value than ordering à la carte, and it is how most working Spaniards eat their main meal of the day.
Tapas
The tapas tradition varies significantly by region. In Andalusia and the Basque Country, tapas are often free with a drink. In Madrid and Catalonia, they are usually paid for separately. The Basque pintxos — small snacks served on bread, displayed on the bar — are a distinct tradition and among the best casual eating in Spain.
Regional Differences
Spanish food is not a single cuisine. Paella is a Valencian dish and is best eaten in Valencia. Cocido madrileño is a Madrid stew. Galician seafood is extraordinary. Catalan cooking is influenced by France and the Mediterranean. Travelling through Spain with an interest in regional food is one of the best ways to understand the country's diversity.