A logo is really a marketing tool that will express the meaning of your brand. Logos need to have the name of your business, possibly an icon and some have a tagline that discuss the brand even further. This visual branding will represent your company on every marketing piece you do as well as be displayed in your office and any retail locations if you have them.
Your logo will be used in different sizes so you need to have it built in a vector format. When I create logos for my clients I build logos in Adobe Illustrator which automatically creates the logo in a vector format. Once my client decides on the design I build out the logo in several versions: black and white, reversed out, and a full color version. I save all in a .eps format for easy transfer into any creative element required for marketing.