find: it searches a specified file or directory in file 
system 
grep: it search a specified string in a file or directory

sed: it replased a specified string.

find is finding a specific file & directory with perm... 
wise,hardlink...

grep : search a specified string on the line. it will take 
from output or file

sed: is a editor tool. using this u can do what u want....

Find : This unix command is used to search for a particular
file in unix directory. Syntax for the same is 
find .* - <file name pattern>


Grep : This command will search for a string/text in
specified file. syntax for the saame is 

grep -<switches> <pattern> <FileName>

there are number of switches availbale for this command.

Sed : its an editor

FIND & GREP
Basically FIND & GREP are the UNIX commands shared through 
the FILTERS .Where is SED (STREAM) is one of the main 
editor.

FIND : Find is an exclusive command used to find   
files/folders are other information.and this is powerfull 
then windows.

ex : # find /raja -name shekar -print
output : raja/shekar


Grep : This is also one of the important command used to
globally searching the regular expression in the file .
GERP is grepping the information character by character.
(i.e) from file .

ex 1) : #GREP "cat" raja 
   2) : #GREP -i "cat" raja (for case sensitive)
   2) : #GREP -v "cat" raja (v represent negative )

OUTPUT :if we have an file raja with data regarding cat we 
can clearly explain.
 

Finally SED (STREAM)

SED : It is an editor but non interactive .
      
ex : # sed -e 'd/chain/dog/f' raja > shekar