An image map is a picture that is subdivided into regions and associated links to other documents, which are loaded depending on which region the user clicks. For example, if you have a Web site selling fruit, you can have an image with several different fruits on it, which can be clicked and used as usual links. This is done by adding a "hotspot" over an area in the picture and then adding a link. This is pretty easy to do with most HTML editors these days, usually by "clicking-and-dragging." Check the manual or help section of your editor to find out how to get image maps to work.
One thing to remember with image maps is to add Alt tags (which show a description when you mouse-over part of the image), especially because there are still some Web users out there who have graphics turned off in their browser, and won't see anything unless you use them.