Eat normally 5 days a week.
“NORMALLY” means normal for an adult. So about 1900-2000cal for an average height woman, and 2400-2500 for an average height man. If you are particularly tall, or short, you may need to adjust that slightly.
Restrict yourself to 500/600cal a day for 2 days a week.
That’s it. for MOST of the population that should be enough to lose weight, if you aren’t losing weight then try calculating your “Total Daily Energy Expenditure” / TDEE and calorie counting the other 5 days and see if you are over compensating on the other 5 days.
You can choose whatever days you want to restrict yourself. You can do them back to back if you want (though it’s not necessary, and Michael Mosely advises against it in the original book).
This diet is NOT recommended during pregnancy, nor during breastfeeding.