When writing code, you could just use Notepad but it doesn't make sense. Integrated Development Environments such as Visual Code provide a host of tools and features including Git integration, syntax highlighting, project management and much more.
Throughout my study, I will be using Microsoft's Visual Code which is available on Windows, Mac and Linux free of charge here. Other IDEs that are commonly used across various languages are Atom, Brackets, IntelliJ and NetBeans. Something more simple such as Notepad++ could also be used to write code if you prefer.
Within Visual Studio Code (VSCode) you can install extensions to aid and enhance any code you may be writing. Here are a few I recommend:
You can also install different themes if you aren't happy with the default dark theme. It's important you are comfortable with the IDE as you are going to be spending a lot of time staring at it. Have a play around with the settings and preferences and look at some of the online resources for Visual Studio Code.