In practical use, where do we actually write the code ? In Microsoft word,notepad ?

Answer 1

For Java, the most use the Eclipse IDE, but there's also Intellij Idea or some other IDEs. Eclipse can be used as Java IDE, but if you install some plugins, you can use it for C++ and other languages, too.

Answer 2

Usually you will use IED (Integrated Development Environment)
https://en.wikipedia.org/wiki/Integrated_development_environment