These two tools are built into your browser
These tools are invaluable in coding, but for design they answer the question "How'd they do that?"
View Source provides the raw files, before anything happens
Shows you HTML, but links to other files like CSS or JavaScript
Right-click to show the contextual menu, then click "View Source"
OR
Command-U or Ctrl-U
Core elements of HTML, and how they're used "in the wild"
How is a page built? Use the find command: Command-F or Ctrl-F to find common elements
One of the most important features is to view and/or link to CSS and JavaScript
This can help you see how others design their files and their code
View Source, but for the DOM, not the files
Updates in real-time
Allows you to edit things like HTML and CSS in-line, as well as run JavaScript in the Console