This book is the advanced manual for BL4NK, the free template for Joomla!™ you can download in current version at GitHub. This book describes in detail how the template works, from the very basic beginning up to advanced usage. Every single line will be discussed. It's the reference work to use on your own template projects.
Software? To understand BL4NK you need an editor. Everything else is optional and up to your preference. I recommend Sublime Text, available in a commercial and a trial version. Free alternatives are Notepad ++ (Windows), TextWrangler (Mac OS) or Gedit (Linux). Two add-ons to make your life easier: the Web Console in your browser and a code library (for example snippets in Sublime Text).
Are you in a hurry? In that case you can find a quick start into BL4NK in chapter "Getting Started".
In the chapter "Blank" the template is described in detail. It is a read only section and ideal for reading leisurely on the couch. However, it wasn't written as entertaining evening reading. For this chapter, you should be wide awake and focused. Read it in your best hours.
A "Bootstrap Tutorial" is also on board.
Still not deterred and eager on template design? Grab a cup of coffee and let's go!