Some customs in Spain are very distinct. Food, for example. Some foods include meat and poultry, venison , smoked ham and chorizo. The sea provides a rich variety of fish and shell fish to go with these dishes.
There's no need for a special reason to go out and celebrate, it's seems like the city is always prepare to go out and have good time. In Madrid, the official fiestas , by calender , are all through the year. It is different from city to city, but basically , you can find everything almost everywhere.
In Spain (and many other European countries), the drinking culture is quite different from that of the US. The drinking age is lower (either 16 or 18) and the bartenders are not that strict either. However, it is not every person's goal (even young people) to get drunk whenever they go out for a drink.
Every year, cities around Spain have a festival called "Carnival", very much like the one in Latin America. This includes drinking, dressing in costumes, drinking, having fun, drinking, and things related to that.