In advanced Russian, the words "надо" and "нужно" both mean that something is necessary. But they are used in different ways. Understanding these differences can help you get better at the language.

1. Formality:

   • "Нужно" is for formal situations. You see it in writing or when people are being polite.
     • For example: "Нужно завершить проект до пятницы." (We need to finish the project by Friday.)
   • "Надо" is more relaxed. It's what people usually say when talking.
     • For example: "Надо купить хлеб." (We need to buy bread.)

2. Subjectivity:

   • "Нужно" means something is necessary because of outside rules or requirements.
     • For example: "Чтобы поступить в университет, нужно сдать экзамены." (To get into university, you have to pass exams.)
   • "Надо" is more about personal needs or feelings.
     • For example: "Мне надо отдохнуть." (I need to rest.)

3. Colloquialism:

   • "Надо" can also show that something needs to happen fast.
     • For example: "Надо бежать!" (We need to run!)

So, while both "надо" and "нужно" mean that something is necessary, the situation and tone will guide you on which word to use. Use "нужно" for formal needs and "надо" for personal or urgent things.