Creating a website can be a very simple activity, or it can be very complex. Regardless, you need to follow several steps:
Decide on a User Interface (UI)
At the most basic level, creating the UI can be done on the back of a napkin. I would not recommend it, but it is a great starting place. Draw out a skeleton of a web page that you want to see. Come up with where you want graphics, navigation, text, advertisements... all components on a page. After you have it in your mind (or on paper), set up a shell page via an HTML editor, and see if it really looks as well in a browser. Don't be afraid to tweak your design at this point. It is easier to change the design before your site is live.
Decide on the pages that you will have
Again, this can be done on the back of a napkin if necessary, but take the time to think about all of the pages you want on your site (e.g. functionality). Be sure not to forget any admin pages as well. Come up with page names, working titles, and think about the type of content you will have on each page.
Write the content for the pages
There are many different approaches to writing a website. The tools most commonly used for simple websites include Microsoft's Frontpage and Macromedia's Dreamweaver. There are also a number of other freeware/shareware programs that help write web pages. These programs provide simple interfaces for people to write web pages.
Many people learn HTML or the other more sophisticated scripting languages. Using HTML you can write the code for the web page as well. Even if you use one of the programs designed for creating websites, you will probably be better off if you learn how to write HTML as well.
There are also a tremendous number of web design and development firms that can create your website for you. They will usually be very comfortable working with lots of different technologies and often can even write the text of your pages.
Preview, Correct Errors, Preview, Publish
Take the time to preview your site before publishing. Whether you use this simple "static" page type approach or have an elaborate dynamic CMS (content management system) in place, take the time before you initially publish the site to browse it. See if the design you came up with really works well as a full website. Again, it is so much easier to fix things before you make your site live.