After you select a map and a location, you can examine an area in which your family members lived or create personalized maps showing, for example, the geographical movements of an individual family member, the distribution of different family members, or the locations of graves.
The Help page shows some sample uses of the site's customization features. Map layers also contain additional information, such as administrative districts. Most of the features appear to be only for the UK, but you can create maps for other locations also. This site, which is for noncommercial use only, is a free offering from a commercial mapping company.