Hello a dad 🙂 Drugs are discovered in many different ways so it is hard to answer this question! In the past drugs have been discovered by identifying the ‘active ingredient’ from traditional remedies (like aspirin, from willow trees) or by chance discovery (as with penicillin). Modern drug discovery involves approached where lots of chemicals are tested against a target in (typically) lots of small reactions all at once. Things that show promise (for example, less fungal growth happened, fungicide seems to be having a good effect!) get tested multiple times to work out what is happening and how safe (or not) something is. I hope that answers your question!