There is a big confusion about naming ship classes in novels and games. But there a consensus that corvettes are smaller than frigates.

What they do in Gc4 is sometimes weird for me as fighter and bombers should be on carriers.

The corvettes should be your first in system vessels. 

The frigates that have hyper drive, upgraded to destroyer (tin cans) then cruisers and finally battleships (very few have ever been built as they are sitting ducks).

Dreadnoughts are a figment of story teller, but OK it's a game!