The phrase "not know the first thing about (someone or something)" means that a person has no knowledge or information about a particular topic, activity, or person.
Here are a few examples:
1. She didn't know the first thing about playing the piano, but she decided to take lessons and learn."
2. I don't know the first thing about gardening. I am allergic to plants.
3. She doesn't know the first thing about football, but she still enjoys watching the games with us.
2. I don't know the first thing about gardening. I am allergic to plants.
3. She doesn't know the first thing about football, but she still enjoys watching the games with us.