How to interpret mtgox chart? What is the difference between red and green rectangle? 

And why there is 0% written in the chart? 

And also, why is mtgox only focusing for 1 month and no more? 

EDIT: The 0% in the chart appears only after loging in.
Green means the price increased during the relevant period, so the lower value is the opening price and the higher value is the closing price. Red is the other way around.

I think the 0% you see is a visual glitch. If you close the charts you'll see that right behind where you see this is the "Volume Discount Display" meter, which shows you how far along you are on the way to move up to the next discount tier. For some reason it is still displayed when the charts are open. (For me the value is different from 0%.)

For charts older than a month you can use for example http://bitcoincharts.com/charts/.