There are an infinite number of ways to intermittently fast. Technically speaking, if you've gone more than 12 hours (including sleep) without eating then: congratulations, you've intermittently fasted! However, there are some popular forms you might want to try.
A good beginner's choice, this diet completes a fasting cycle every twenty four hours — its numbers referring to the hours in each phase. You spend sixteen hours fasting each day with an eight-hour break for food. This break can be at any point in the day, as long as you have sixteen continuous hours of fasting.
Other ratios using this format are often discussed in the fasting community. Typically, the fasting number is placed first, so technically speaking, a twenty hour daily fast would be "20:4," but this includes the sometimes jokingly called "4:20 Diet."
OMAD stands for "one meal a day." With this diet, you consume all of the calories you are going to consume each day in one sitting and then immediately begin fasting once more. Be careful to get enough nutrition. Without some monitoring of your diet choices or supplementation, you run the risk of dietary deficiencies.
This is effectively equivalent to something like "23:1" (or even if 23.5:0.5 if you eat like you're on in speed eating competition).
If you see numbers that don't add up to 24, but do add up to 7, it's instead a weekly plan. This involves eating regularly most of the week but engaging in 24-hour fast two days out of the week, which should be done non-concurrently!
There are an infinite number of ways to intermittent fast — these are just some popular choices. Some people aren't rigid with their schedules and may vary their fasting length on a day by day basis based on various factors in their life.
If you're looking for tips about how to hone your fasts to work best for you, the r/IntermittentFasting subreddit may prove helpful, as it has a highly active community.