A logo is the "image" or identifying mark of a company. Graphic images on a web site usually incorporate a company's logo to create a corporate identity, image, and consistency for web pages.
If your company does not already have a logo, you may want to work with a graphic designer to create one, although a logo is not absolutely necessary.
You may need photography on your web site. Portions of a photograph can even be made "click-able" to link to other web pages or sites.
Banner ads are those "advertisements" that you see on the Internet, which can be many different sizes and shapes. Standards have developed, and the use of banners is useful for bringing web site visitors to sites they want to see.
Graphics, used properly, can add visual appeal and clarity to the message of your web site.
The Website 101 pages are basic informational pages to provide an overview of some of the more standardized functions of most web sites.