WDI Fundamentals Unit 2
Sublime Text is a free text editor used by developers. Check out the following video to learn how to download, install, and use Sublime Text 3. You'll need it (or another editor like it) to write code on your own.
Another popular option is Atom, an open-source text editor created by the makers of GitHub. There's a great tutorial on how to download, install, and use Atom here. Both these editors are free, so you might consider testing which one you like best.