Alexa Ranking

Two of my blogs got a big fat zero on Alexa Ranking and because of that, I am unable to take some highly paid opps. Today, it was a $35 deal *sob sob*

I can honestly say, I do not know what Alexa Ranking is and how it works. I only heard the figure can actually be manipulated and is not really accurate. If anyone care to enlighten me about this, I'll really appreciate it.