Cover 2, the safeties are Spread out REALLY wide. Usually outside the hashmarks.
The corners are also close to the LOS.
After hike, the corners dont drop back, the Safeties stay out wide.
as for Cover 3, Usually its one safety( most of the time the FS) thats deep out, the SS is hovering a yard or 2 above the Linebackers most of the time(Hes usually in a yelow,purple or Light Blue zone) this can also be flipped with the FS down low. the Corners might be up close, might be far back. They Always drop into deep blue zones in cover 3.
Im sure I made a mistake some where along the line of explaining this, Im sure more people can add on and help you out.
Subject: need help with reading the D