Bruno -

The tutorials are really helpful. Once you play around with the way they use nodes, it makes sense. The videos are short, but to me were clear. While I had reviewed 2.5, I hadn't used it in a while because I was doing other things, so I had to refamiliarize myself with it.  Parts of it were also brand new. The various tutes led me through it. Once I understood what I was doing, I could apply it.