MDN HTML

The page describes what HTML is, then provides key resources to use such as basics, an area for tutorials, a reference section, and an advanced topics section for those that have worked with HTML quite a bit. I would use this information whenever I need to quickly remember how to code something, as its difficult to remember how everything works in code. I would use the MDN for HTML information as they have plenty of available information, and the source seems trusted and reliable to use.

MDN CSS

The article on the MDN website describes what CSS is, and how it is used in conjunction with other code languages, such as HTML and XML. The website offers several key resources for anyonee to use, such as tutorials, references, a cookbook to be able to "bring recipes for common layout patterns" and other tools for development for CSS. I'd use this website as CSS can sometimes be very confusing to try and specify what you want to be done, and finding out what you need to use right away is extremely useful.

Conclusion

When looking for help in relation to programming, it is essential to have a trusted source that you can always fall back onto when you need some help. Trusted sources know their information, and are solely looking to provide information to users and help those out that need help. Non-trusted / unreliable sources can cause you to have errors in your code, or not specify how something works so it doesn't provide much help. It's important to know what exactly you are coding, as untrustworthy websites may have sketchy ways of implementing features that could cause your website or program to be uneccesarily bloated.