Примерно:

function PostData(PostData:String):String;

var

  SPostData:TStringStream;

  SResultData:TStringStream;

  HTTP:TIdHTTP;

begin

  SPostData := TStringStream.Create(PostData);

  SResultData := TStringStream.Create('');

  HTTP := TIdHTTP.Create(nil);

  try

    try

      HTTP.Post(URL, SPostData, SResultData);

      Result := SResultData.DataString;

    except

    end;

  finally

    SResultData.Free;

    SPostData.Free;

    HTTP.Free;

  end;

end;



PostData('text=alabala');