catch keyword. If while handling an exception you want to display an error message to the user, you can use GetFormattedText(), a static member function of TExceptionFormatter:
catch (const TMyException& exception) {
TStandardText message;
// currentLocale is for internationalization - specifies the language to use
TExceptionFormatter::GetFormattedText(exception, currentLocale, message);
// display message to the user...
}