In high school, but the very basics. I didn't truly understand my menstrual cycle until I was at university and decided to learn the fertility awareness method for contraceptive purposes. When you begin charting your cycle and tuning in with yourself each day, you learn so much about your own unique menstrual cycle and your overall health.
Learn the fertility awareness method and begin living in alignment with your cycle. I am a certified fertility awareness educator and I truly could not speak more highly of the profound connection you find with yourself and your cycle once you learn this method. Living in alignment with your cycle is something I speak about regularly and hold workshops on. It basically means choosing to eat, move and practice self-care in ways that serve your hormones at each part of your cycle so you can feel your best and function at your most optimal.
Conversations at home, at school, in the media and with friends. Chatting about your period openly and not feeling ashamed is what will reduce the taboo around periods. I think generationally it is changing and we are much more open about talking about the menstrual cycle than my mum's generation for example.
I don't particularly like apps as many of them are algorithm-based and predict your fertile window from past data entries. This can be very misleading as many external things such as stress, travel, or illness can interfere with when you ovulate. This can be dangerous if you are trusting this data for contraception and at the very least upsetting if you are using it to predict when you are fertile for conception. I prefer paper charts although if you are just using your period app for data entry of symptoms that is perfectly fine. I use CLUE but I have heard that Flo and Kindara are quite good.