Basically, intermittent fasting simply extends the time between meals. Mostly, this concerns the time between dinner and the first meal the next day. Most people thus simply do without breakfast the next morning and then only have lunch again. For example, if dinner is finished at 8 p.m. and then not eaten again until 12 a.m. the following day, the body can benefit from a 16-hour period of fasting.
However, these times are not fixed and can be introduced individually. Some people simply alternate between a "normal" day and a real fast day.