HTML is very similar to word processing in structure. For a start, HTML differs from programming in the sense that it is processed sequentially, as opposed to programming languages that use commands like GOTO to jump forward and backwards within the source code. This means that what processes the code- the internet browser, in this case- reads from top to bottom, like someone might read a book.

HTML consists of 2 data types: content and tags. Content is what you seem on in your browser - text, graphics, etc. Tags are the code than affect and alter the content, like the underlining of text in a word processor document. They cannot be seen when viewing the document in a browser, but their effects can.