If you did the introductory tutorial you know at least one editor.  Text editors such as Notepad, vi, nano etc. allow you to type plain text in.  HTML, CSS and JavaScript are all just plain text so they seem ideal.  There are some possibly better options though:

In this tutorial you could use a simple text editor but it is recommended you try a more specialised code editor such as Notepad++, Sublime or Eclipse.  There are many others to try so you should eventually try lots and pick the one that suits you.

If you are not sure at this stage start with Notepad++.  For ultimate flexibility get an external hard drive (or a USB flash drive if you don't mind the speed) and install PortableApps.com on it.  This is a collection of software which you can use from the external drive without installing on the computer.  That means you can use them in lots of different places (e.g. at college, work and home) and not need to synchronise data and settings.  Portableapps has a number of html/css/code editors available but start with Notepad++.  If you don't need the flexibility of using the same editor in many places just get the installable version of Notepad++.

Notepad++ is small, quick and offers the key features which help with coding (tabs and syntax highlighting being the best two for a beginner).  You can also add more functions later if you need them.  Sublime may be a better editor for some. Eclipse is a very powerful monster probably avoided for now.  Try it later on though.