So far this semester, some of the things you have learned include;
This week we will start learning about and exploring CSS or Cascading Style Sheets.
CSS is a language that tells browsers how to display and style content in HTML. It will not change the content itself, but will allow you to specify color, font, size, background, padding, alignment, how pages resize, if certain elements should be hidden, and many more qualities.
Read the w3schools short page on what CSS is, and why it exists.