The HTML is the code that browsers use to read and display the format and content of a web page, and is basically used for the structure and static content of the page
CSS is a language for additional stylistic markup that is less unwieldy to work with and also allows you to define styles that can be referenced later in the HTML code
Javascript is a code that allows you to create functions which are used for manipulating data and elements within your webpage, such as anything that requires active calculations and updates.
The 'i' tag formats text into italics, the 'b' tag formats text as bold, the 'h1' tag formats text according to the style of the first-tier headline, and the 'li' tag contains a list item belonging to any type of list
the 'br' tag requires no end tag, and it is used to add a paragraph break (blank line of text)
Selectors in CSS are snippets of code that relate the CSS you create directly to a certain type of HTML code. An element selector is a selector that causes your CSS to impact every instance of that element on your page, for example saying that every single time a h1 tag is used it should have a certain font size and color. An id selector only applies the CSS styling to elements that have explicitly been identified by that id, so we can give names and custom formats to special or unique portions of the page. A class selector is similar to an id selector in that it only affects certain elements we choose, but instead of affecting a certain id'd element it allows us to apply formatting to any of a 'class' of elements which we can define by explicitly telling the HTML element that it belongs to that class.
I made all my paragraph text red by adding a CSS definition for p saying 'color: red' into the style section of the header.