TEdit has an OnChange event, which fires every time you add or delete a char in an Edit component. If you add this event (e.g. via Object Inspector), you can read the text value as a string (so yes, you're right).
procedure TForm3.Edit1Change(Sender: TObject);
begin
Form3.Caption := Edit1.Text;
end;
If you try to get numerical data, you should try to convert it in this procedure, but be careful. You should always validate user's inputs before working with them, and prepare your application for incorrect formats. This example tries to convert the input to an integer and a real variables.
procedure TForm3.Edit1Change(Sender: TObject);
var i: integer;
x: real;
begin
i := StrToIntDef(Edit1.Text,0);
if not TryStrToFloat(Edit1.Text, x) then x := 0;
Form3.Caption := 'Integer: ' + IntToStr(i) + ' Real: '+FormatFloat('0.##',x);
end;