RAISERROR function will generate error in the TRY CATCH block:
DECLARE @msg nvarchar(50) = 'Here is a problem!'
BEGIN TRY
print 'First statement';
RAISERROR(@msg, 11, 1);
print 'Second statement';
END TRY
BEGIN CATCH
print 'Error: ' + ERROR_MESSAGE();
END CATCH
RAISERROR with second parameter greater than 10 (11 in this example) will stop execution in TRY BLOCK and raise an error that will be handled in CATCH block. You can access error message using ERROR_MESSAGE() function. Output of this sample is:
First statement
Error: Here is a problem!