What is CSS?:
CSS is a programming language used to define how web pages will look. HTML is used to tell your web browser what content to display on your web (or blog) pages while CSS defines the presentation of those HTML elements (how they'll look, including colors, sizes, placement, etc.).
What are Style Sheets?:
A style sheet is made up of various rules that you modify to make your web pages look the way you want them to. A complete website is made up of a group of style sheets that work like a waterfall does where one cascades to the next. In other words, rules from one page follow to the next in a type of hierarchy of rules the visual presentation will follow.
Do I Need to Learn CSS to Start a Blog?:
The short answer is no. However, if you want to be able to customize your blog without paying a blog designer, then learning CSS can be an invaluable tool.
Where Can I Learn CSS?:
You can learn CSS through online tutorials and books. You can follow the link to find 10 popular resources to learn CSS.