MDN HTML
On the HTML page, it provides information on the basics, listing elements with links to explain each in further detail. They also have tutorials and references for every element and attribute. This is a great way to remember and get an example of elements and attributes you may have forgotten or don't have much experience using.
MDN CSS
Similar to the HTML page, the CSS page explains the basics of CSS, tutorials, and references for every property and concept. They also include a 'Cookbook' for basic layouts that anyone can use. This page has a lot of information that can be useful for anyone looking to learn or remember things.
MDN DOM
This page doesn't explain much. It shows a lot of interfaces that I have no clue about, but I do recognize SVG. A lot of the elements show what is compatible for each browser, and gives an explanation on them. This page may be useful eventually, but I currently know how I can use the website.
MDN JavaSript
This page is also like the HTML and CSS pages. It has a lot of information, tutorials, and references to help teach you about JavaScript. There are tutorials for more advanced topics, and also tools and resources to help debug JavaScript code. I think this will be very useful the further I get into class, because all the information I might need is on one page.
Summary
Trusted resources are very important for programming help. You may be coding for security and be shown an old way of coding that leaves a bunch of holes. Having a trusted resource can keep you up to date and show you new ways to fix a problem you may not have thought of. This can also help for search engine optimization.