N: you are a non-EU resident and purchase goods in the EU for personal use in your non-EU homecountry
E: you export the goods to your home country before the end of the third month after the month of purchase
M: you spend a minimum amount per shop, per day
S: you have received a stamp from customs on your receipt, either at EU-customs or at a customs office upon arrival in your home country
Please note; there are also requirements for purchase receipts.