[achal]

> 'a,'b

Between mark `a' and `b'

> g/fred

If the line contains the pattern Fred, execute the following command (s/dick/joe/igc)

> s/dick/joe/

Replace dick with joe

> /igc

i: Case insensitive

g: Replace multiple occurrences on the same line

c: Ask for confirmation on each substitution

I may be wrong about some detail, but I believe that's it.