I don't have a degree in economics, but this is good news for Brazil. Other countries can feel confident about lending money to Brazil at a good interest rate. If you fall below this status, you as a country are almost bankrupt, and you can't borrow money. Your shares are considered "junk bonds" or something like that. So Brazil, like many countries, must borrow money, and their debt is huge, but it is good news to have an investment grade rating. It must be like a person having a good credit rating.

I am a business student, but I have not taken economics. However I think I can explain this "Brazil became a net external creditor and two ratings agencies awarded investment grade status to its debt. " The ratings agencies applied a status ( rating/ranking) the debt of Brazil.