Buses are just as popular in Barcelona as the Metro. They can sometimes take a bit longer as they are forced to deal with road traffic, and they run a little less frequently.
The TMB website has a trip planner http://www.tmb.cat/en_US/home.jsp in English. If you are dedicated to riding the bus, you can elect only to use this form of transport when you input your details.
If you are looking for a complete bus network map of Barcelona, you will be disappointed. Even the TMB´s site only offers maps of individual lines. If you know your own local bus line number, you can download its route map here by using the dropdown boxes. http://www.tmb.net/en_US/barcelona/moute/planols/planols.jsp
Generally buses operate from around 5:30am to 11 pm, with buses arriving at least every 20 minutes or so. Depending upon routes and traffic patterns, buses can sometimes take more or less time.
The fare system is basically the same as the Metro (see info below). You can buy tickets for individual journeys for the bus at about €1.40 Euros per ticket when you board. Buying tickets one at a time is not recommended unless you are only in Barcelona for a day. The best option is the the T10 ticket. You can purchase your T10 ticket at any metro station or online at: http://www.tmb.cat/en_US/home.jsp. You can purchase individual or multiple rides on the bus itself and your driver will be able to make change – provided you pay with bills of 20 Euros or smaller.
The T10 ticket costs €7.95 for ten trips within Zone 1. You can buy T10 tickets for other zones as well, but most of the districts in Barcelona are covered by Zone 1. A T10 is valid indefinitely within a calendar year (however the card will expire one month after the new tariffs are released in January each year) and you can share the trips on your card with other people travelling with you at the same time. It is valid on the Metro, buses, trams and trains within the nominated zone.
A tip for using the T10: If your journey is less than 1.25 hours, you can use a single trip for all the forms of transport you take. For instance, you can change trains at Metro stops (as long as you don´t leave the underground), then leave the metro and jump on a bus to finish your journey or vice versa as long as the total length of the journey is less than 1 hour and 15 minutes.
Depends on your line and station. City center stations might run more frequently than a bus servicing the outer edges of the city.
You must always board the bus at the front entrance and either purchase your ticket through the driver, or swipe your card through the reader. As you exit, you must always exit in the middle or back exits, never through the front. The driver will always enforce these rules, too.
As you see the bus approaching your stop (and if you want to board), flag it down in advance by waving your hand. Otherwise, it’s not always guaranteed that the bus will stop at your stop. All buses are clearly marked at the top by their number, and at each bus stop, there are maps of each of the bus lines that stops at that particular location.
Give up your seat for the elderly, or pregnant women, if it is crowded. It is normal for someone getting on the bus (usually an older person) to give a loud greeting to all passengers when they board. It´s polite to return the greeting, or at least smile and nod.