SQL & PL/SQL

Hi
When i tried to know about what exactly "db block gets" and "Consistent gets"
are, i ended up gettting really confused. some document say "db block gets" are
read in "current mode" and "consistent gets" are read in "consistent mode", but
there is not much information about the two modes, when i tried googling i couldnt
find much much about that, can some clearly explain(like a lay man kind of
explanation) me what they are all about.

whether they are good or bad for a query, in which scenarious we will get
more counts for "db block gets" and "consisten gets" and how to manage that.

Thank you
Maximus