One way to find things is to use the vba equivalent of the Find command under
the Edit menu.  If that appears appropriate then it would be something like
this:
set rng = columns(1).Find("ABCD")
if not rng is nothing then
  msgbox "abcd found at " & rng.Address
else
  msgbox "abcd not found"
End if

The find command has some persistent arguments, so it is best to set them
all when you use it.  I have just used one for illustration.  See the help on
the find command or easiest is to turn on the macro recorder and do a find
manually.  Then turn off the macro recorder and view the code.  Then modify
the code so it operates as I have above - rather than activating the found
cell.

I also illustrated how you can use the address function to see the address,
however, usually what is more useful is

rng.row
rng.column
to get the row number and column number.

In the first part of your description it sounds like you want to actually
loop through a known range, then react to the values you find there.

for each cell in Range("A1:A20")
 if not isempty(cell) then
    set rng = columns(5).Find(cell)
    if not rng is nothing then
       msgbox cell.value & " found at " & rng.address
    else
       msgbox cell.value & " not found"
    end if
  end if
Next