A map book is like an atlas: it takes a single map and divides it into "tiles" by placing a grid over it. Each square of the grid becomes a map tile. Each tile is then rendered on a separate page, which you can publish to a plotter or to an electronic format called DWF. Once you publish a map to DWF, you can share it with people who do not have a copy of AutoCAD Map 3D. These people can download , a free viewer available from http://www.autodesk.com, to see the maps.
Map books use viewports to organize the information on each page. A viewport is like a frame on a web page. You can create a custom viewport as an on one or more of the map book pages. Pan and zoom within that viewport to display an enlarged detail of the map.