If you are interested in doing a short visit of about two or three days you can walk the city centre, the main quarters there and enjoy its artistic buildings , churches and cathedral, Gaudí Arquitecture and Picasso museum as the most relevant in barcelona. You may also see the Ramblas and the typical markests. I you wnat to see the sorrounding area of Barcelona it will take your more days. Here we include a link where you can see itineraries for a different amount of days.

http://bit.ly/aflh3T