Unless you want to learn how to program, you will need to download and use a good HTML Editor. An HTML Editor is tool that generates a computer program in HTML using a sophisticated word processor. There are plenty of good HTML editors available and many are free. They are sometimes called "WYSIWYG HTML Editors" (What You See is What You Get).
To build a more professional website, consider a more sophisticated package like Microsoft Expression Web or Dreamweaver MX. These feature rich products can help you create very attractive and easy-to-maintain websites. Microsoft now provides Expression Web 4.0 free.
Once you have downloaded the program file, you'll need to install the HTML Editor on your machine.