As you walk into the various pinxtos bars of the area, chefs line the bar with various dishes that you can pick and choose from. Then, when you're ready to pay your bill, some will count the number of toothpicks, or in San Sebastian, many are on the honor system and you tell the hostess how many you ate. Most pinxtos run for under two euro's, so you can eat relatively cheap.
Here's some pics of my favs:
SagardiThese were from Sagardi (in the Ribera District near the Picasso Museum) in Barcelona - a great recommendation from Rick Steve's. Here we got a variety: a mini leek quiche; croissant with jamon; baguette topped with goat cheese and a red pepper; baguette topped with tuna, shredded cheese, cherry tomato and anchovy; a "Gilda" (see below); and a chorizo pinxto.