And this is the beginning of a paragraph. HTML tells the web browser what the content is. It says "Hey, this text is an important heading! That text is a less important heading. This is a link! That is an image." And so on. It is useful, because computers don't get subtlety. You need to tell them things explicitly. That's why computers make bad boyfriends. You have to spell everything out for them.
HTML Stands for Hyper-Text Markup Language. Hypertext is the text inside of hyperlink tags. And Mark-up Language refers to all the notes saying "Hey computer, this is a heading!".
HTML creates the content for all webpages. This is what plain HTML looks like without CSS. It's kind of ugly, but it gets the job done. The browser will pick the font, size, and spacing for you.
Click here to see what CSS can do.