It's rare to find yourself more than a minute away from a bar or café in the centre of Barcelona, and it's rare to find a Barcelonan of any age or sex who hasn't popped in one at least once a day to their local for a quick breakfast or aperitif.
Note that almost all cafés served drinks and almost all bars serve coffee; cafés are generally more likely to have terraces or indoor seating. If you sit outside, you'll usually be expected to pay when served; standing at the bar, you usually pay when you leave.
While cafés general stay open all day, bars tend to have their own whims; many do not open until 3pm or even later, and stay open late. Note that even if bars officially close at 2 or 3am, but if the ambience is good the owner will close the door and let the party continue inside.
The coffee is good and available nearly everywhere. Order it in a variety of ways:
Image by frank müller