The British National Formulary is like a special book that has information about different medicines that doctors can use to help people feel better. It's a big book with lots of pages and all the information is organized really neatly so it's easy to find what you're looking for.
Think of it like when you go to the library to find a book. All the books are organized by subject and then by author name. That's kind of like how the British National Formulary is organized - all the medicines are grouped together based on what they do to help people's health and then they're listed in alphabetical order.
The book has lots of different types of medicines in it, like pills, liquids, and injections that go into people's bodies. Each medicine has a name, just like how you have a name, and the book also tells you what it should be used for and how the medicine works to help people who need it.
Some medicines are only for grown-ups, and some are for kids too. But it's really important that only doctors and nurses use this book because medicine can be really powerful and can cause problems if it's not used the right way. So while the British National Formulary is really helpful for doctors and nurses, it's not a toy to play with at home and only grown-ups should use it.