When you see a tag that has a name followed by some other words, each followed by an equal sign, those other words are parameters. Some HTML tags are called grouping tags. These tags can contain other lines within them. Such beginning and ending tags are also used for formatting. That's all there is to it.
Pages contain text and formatting and organization commands, called tags.
To understand HTML, you need to know the key tags. The capitalization of tags doesn't matter. Inc. All other trademarks are the property of their respective owners.