Greetings salaatti ,
There are several approaches to Theravada meditation and different teachers emphasise different things, so what they say is bound to seem contradictory since they are trying to keep it simple by only telling you what they find is most helpful for their students in the approach that they teach.
Ajahn Brahm is teaching a concentration practise and his instructions to just have a general idea of breathing in or out are excellent for that. Others are teaching with more of an "insight" orientation, where you want to be focussed on the actual sensations.
If you are a beginner then my advice is to follow the instructions of your teacher (or a particular teacher's book/web site, etc) for at least a few months. Once you have an experiential understanding of one approach it will become much clearer.
For example, if you want to use Ajahn Brahm's method then go to and download the first few chapters of his book, Minfulness, Bliss, and Beyond (click on the book on the home page) and order a copy. Go to the guided meditation podcasts and download some of his guided meditations.
If you want to use Bhante Vimalaramsi's method, go to and download his instructions, guided meditations, etc...
And so on...