In Spain, breakfast tends to be light. The main meal is eaten between 2 and 4. It would be difficult to find a place to have a sit down meal in the afternoon before or after those times. That said, small dishes abound. Tapas are served when drinks are ordered. Potato chips (patatas fritas) and olives (aceitunas) tend to be fairly common. For something more substantial, order a ración (portion) or media ración (half portion) from la carta (menu).
The evening meal is much lighter than the afternoon meal. Tapear (eat tapas) is a great way to try lots of different things in the evening.