The 4.5 million digital images comprise birth (1889 to 1930), marriage (1889 to 1950) and death (1889 to 2006) records from all cities in the state of Rio de Janeiro. The index isn’t completed yet; you’ll need to browse the record images by place in the free Record Search Pilot.
PS: And if you get stuck while trying to climb any language barriers, consult FamilySearch’s Portuguese Genealogical Word List. (Which is actually more than just a list. Don’t miss the links at the top to different parts of the guide).