You can get the train by catching one at the airport station and changing at Barcelona Sant. The trains to Sant are every half hour or so and you can get the train times, price etc from Sant by checking out the RENFE website.

As for the bus, well there are different ways of doing that. You can catch a bus from the airport to either Reus or Tarragona and get a taxi from there (check out the Alas.es website for times and prices), use one of the shuttle bus companies such as Resorthoppa which offer a service direct from the airport to your holiday (costs around £21 per person return) but to be honest I used that earlier this month and found it a little bit too hit or miss for my taste or use a tour company such as Touchdown Tours who are based in Salou, English owned and again offer a door to door return service but tend to be a little more expensive depending on how many are travelling ie the more of you there are the less per head it will cost.

Hope this is of help and that you have a great time. We sure did!!