1042-S is issued to taxpayers who are subject to foreign persons and taxpayers who are subject to backup withholdings because there is no W-9 on file.  How you report the income and withholdings is no different from how you'd handle W-2 or other 1099's but you will need to refer to the 2-digit code in Box 1 for the type of income.  In the event it is a recurring payment and the recipient is a US person (i.e. resident alien or US citizen/national), he or she should contact the payor asap to ensure a W-8BEN or W-9 is on file.