what did you not understand?
To get a stamp after change of status to a different category of visa (like F1 to h1), you have to go visit a US consular post, all of them outside US. It is not necessary that you have to get it from a US consulate in your home country.
St.Louis (formerly dept of state washington) can be used for revalidation of visas (eg:- H1 extension..)
And Brazil has a US consulate office in Rio De Janiro...