Spain is quite a big place, and the traditional food varies regionally.
In the South, i.e. Andalucia, then historically you have quite a lot of Arabic influence from the Moors, while in the north it is closer to French, although rarely as fussy and overdone.
Some things are universal. Pork and ham are used in absolutely everything. There is a lot of seafood, olives and olive oil, and some fantastic Sheeps cheeses.
Like Italian food, Spanish cooking is normally really quite simple, with all of the flavour coming from the fantastic ingredients that are available.
Some stereotypical Spanish dishes would be paella, gazpacho, and tortilla (potato omelette).