This function can be accessed in the File toolbar or the File Menu
The Download Online Imagery/Topo/Terrain Maps command allows the user to download mapping data from numerous built-in and user-supplied sources. This includes access to worldwide street maps from OpenStreetMap.org, as well as seamless USGS topographic maps and high resolution color satellite imagery for the entire United States. In addition, access is provided to several built-in WMS (OpenGC Web Map Server) databases to provide easy access to digitial terrain data (NED and SRTM) as well as color satellite imagery (Landsat7) for the entire world. You can also add your own WMS data sources for access to any data published on a WMS server.
This is an extremely powerful feature as it puts many terabytes of usually very expensive data right at your fingertips in Global Mapper for no additional cost. Note that this feature requires Internet access to work.
When you select the menu command, the Select Online Data Source to Download dialog is displayed. This dialog allows you to select the type, or theme, of data to download, as well as the extents of the data to download.
Click Here for more information on Importing Online Imagery.