MDN HTML
HTML also known as (HyperText Markup Language) defines the meaning and structure of web content. HTML uses markup to annotate or interpret content on a page display in the Web browser. There are common elements we use which include head,title,body,header,footer and many more. Each element has to have tags (opening or closing) for the element to appear correctly. HTML is vital when creating web pages and understanding HTML is quite easy if you make sure to include opening and closing tags around each element. The MDN HTML provides a great overview of HTML as well as all of the elements that have opening and closing tags.
MDN CSS
CSS is stylesheet language that is used to describe the appearance of a document/page when written in HTML. CSS allows you to decide how elements should appear on the screen as well as any styling features you want to use. Examples of styling could be used to change the font, size, color, spacing, animations and many more. MDN CSS provides a useful page all about CSS as well as several tutorials on beginner CSS steps as well as more advanced tutorials and tips.
MDN DOM
Document Object Model or (DOM) is an API (Application Programming Interface- a set of features and rules that are inside of a software program that allow it to interact through software). The DOM API represents and interacts with HTML documents and loads through the browser. DOM on MDN provides helpful information on documentation with the Document Object Model as well as standards of the DOM.
MDN Javascript
Javascript is a programming language that uses first-class functions, meaning the functions are treated as any variable so functions are able to be passed to other functions and returned back and can assign a value to a variable. MDN Javascript provides a great variety of examples of assigning a function to a variable as well as passing a function as an argument.
Summary
Trusted resources are so important when creating a site, it can be very easy to click on the first website you see when you are confused however there are certain sites that are better than others because they are trusted by most. Trusted resources include W3schools, MDN and CanIUse.