Объясните задачу Delphi. Задача сделана только код я не понимаю!!

[LudaBojar]

procedure TForm1.FindDialog1Find(Sender: TObject);
var
Found: LongInt;
S_Pos, End_Pos: Integer;
begin
with RichEdit1 do
begin
if SelLength <> 0 then
S_Pos := SelStart + SelLength
else
S_Pos := 0;
End_Pos := Length(RichEdit1.Text) - S_Pos;
Found := FindText(FindDialog1.FindText, S_Pos, End_Pos, [stMatchCase]);
if Found <> -1 then
begin
SetFocus;
SelStart := Found;
SelLength := Length(FindDialog1.FindText);
end;
end;

end;