The warm climate makes for some fevered nightlife in Spain, and if you want your gap year to be packed with parties it's the perfect destination. Spend your days backpacking around famous sites and cities, and when night falls travel to a bar, club, pub, or whatever takes your fancy. Just be ready to keep going into the small hours.
If you're looking to meet people in Spain, you should find a good bar or two. They're a massive part of the nightlife culture, and even in the middle of the week you'll find them packed with people. They don't even have an age restriction for entering the premises, though anyone under 18 won't be served alcohol. This means you'll sometimes find families chilling out in buzzing bars.
As you might have gathered by now, things start a lot later in Spain than you might be used to. On weekends a lot of people won't start their night out until 11pm, so if you go earlier you might find yourself in an empty bar.
It's also worth remembering that bars in Spain often aren't as rowdy as you might be used to. For many they're a place to relax after work or studying, with a drink or two and some tapas. It's not as common to see people getting very drunk, though of course this varies, and you're much more likely to get away with it in big cities.
Wine bars are a more sophisticated alternative to normal bars, although the principle is the same: a relaxing drink and a small tapas dish.
If you're after a glass of red ask for 'un tinto, por favor." For white wine ask for 'un blanco, por favor.' If you're a rose fan, ask for 'un rosado, por favor.' Sorted.
There's a big clubbing scene in Spain, especially in big cities like Barcelona, Madrid, Valencia, etc. Nights out clubbing usually kick off a lot later than elsewhere in Europe, with some clubs not even opening until 1am and not getting busy until 3am. Again, this will vary depending on where you are - the more tourists present, the earlier a night is likely to kick off. If you're doing things the Spanish way, you can expect to be out until sunrise.
For a proper Spanish experience, finish off a night of drinking and dancing by going for breakfast and ordering chocolate con churros, freshly fried fritters that are dipped into warm chocolate sauce. It's not quite a kebab, but it's still immensely satisfying.