Microsoft SharePoint is a family of software products developed by Microsoft for collaboration, file sharing and web publishing. One purpose is that it can be used for, in small business, is as a company intranet or internal portal. I like to think of it as a way to visualize the data that is inside of department/company folders. One of the triggers I ask clients is whether they are finding they are spending a lot of time trying to find documents.
Here is a good introductory article on the CMIT Solutions blog that is worth reading too to understand SharePoint.
Since one of the key aspects here is visualization, you can understand more about SharePoint is and what is can do from the following videos.
1. Good Introductory Video explaining what SharePoint it is.
2. See a sample SharePoint site. This video is geared toward end-users that explains the structure/concepts of a SharePoint site.
4. Overview of a sample SharePoint team site and some end-user basics. Features covered are: announcements, calendar, document management, document templates.