Bb/100 and EV bb/109

So, I am trying to compile stats on myself to focus on areas to improve in my game. I looked at the terminology thread and noticed bb in this case means big bets. What would be considered a big bet? I am assuming the program I am using is projecting the expected value for me in the EV bb/100 column. What would cause a 41.30 bb/100 stat to produce a negative 5.02 EV bb/100 stat? How do you use the bb/100 stat to predict EV? Any good books on this topic?

Livro não, mas tem excelentes instrutores no Brasil e grupos de discussões também é muito bom.