So, a natural FET cycle goes as follows: You call your clinic on Day 1 to let them know you've started your cycle. They will tell you which day to come in for a blood test. It's usually around day 9 but can vary according to your cycle length. Then you'll have blood tests either every day or every second day, looking for your hormone surge which indicates you've ovulated naturally. As soon as they get the level they want, they stop testing your blood and give you a date for transfer. If you have embryos frozen at day 3, it will be 3 days after you ovulate, or 5 if that's when they were frozen. You show up for your transfer (praying like mad something has survived the thaw!), they pop it in, and that's it. You don't do anything more until your pregnancy blood test. Unless you cheat and POAS first, which I did, hahahaha!
Obviously every woman is different, you may end up on some hormone support or may be changed to a medicated cycle, where your ovulation is triggered with needles, but if you are going with a totally natural cycle then that's all there is to it. Good luck!