Cascading Style allows obtaining the full control under HTML tagging. CSS allows easily redefining the all default properties of any HTML tag. Using CSS you will open new unique opportunities missing in common HTML.
For example, by means of CSS it's possible to set the tracking between characters and space between text rows. Using CSS properties you can exactly specify the background image position disallowing the repeating of the image within the document.
Using CSS you will create new HTML pages much faster. The styles that were once determined can be used again and again in any part of the HTML document. It's very important to understand that using CSS in external file gives a chance to change properties for all elements in any pages where this style definition is used.
This web-site contains the base steps which will allow you to know about CSS a little more. I sincerely hope that this stuff will help you skilfully use the power of CSS in your web-projects.