HTML, or Hypertext Markup Language, is sort of the grandfather code of the Internet. It's probably the most recognized "language" and it is what browsers render to make page readable to humans and "interactive". Even though WordPress uses other fancy code languages such as PHP and CSS, it's actually using these programs to basically generate standard HTML.
From a non-coder perspective, HTML is probably about the easiest to understand as basic HTML can almost be deciphered just by looking at it.
Students often get hung up with WordPress whenever they need to make a few basic HTML changes in the post/page editor. Knowledge of a few, very basic HTML commands can put a WordPress beginner on the road to mastery. Just keep in mind, the majority of HTML requires some type of opening command followed by a closing. This may not be the correct term but I like to consider it symmetrical. If it opens on one side, it needs to be closed on the other.
I've outlined a few HTML snippits that I think every WordPress Bloggers should know by heart. If you're interested in learning more, I recommend a website called w3schools.com.
A HTML Link:
<a href="http://chicagowptraining.com">link text</a>
A HTML Image
A HTML Image + Link
<a href="http://chicagowptraining.com"><img src="/wp-content/uploads/2014/05/name.jpg"></a>
An image with WordPress attributes:
<a href="http://chicagowptraining.com/wp-content/uploads/2014/07/test.png"><img class="alignnone wp-image-726 size-medium" src="http://chicagowptraining.com/wp-content/uploads/2014/07/test.png" alt="alt text" width="300" height="111" /></a>
A HTML Break
<br> - note, a closing is not required.
Other HTML Styling
Headings: <h1>Heading 1</h1> <h2>Heading 2</h2>
Feeling daring? Open up a recent post and select the "text" tab to the right top of the WYSIWYG Editor. Spot the HTML snippets that I outlined above.