What is the Map Module? The Map Module in Lightroom lets you see where your photo's were taken in Google Maps. It is also a place where you can put the GPS coordinates on your photos.(Geotag) This can be a great tool for you to see where you take the most photo's at and if your a landscape photographer like me and you've hiked in many miles and you don't really have a address to put your location down you can geotag these photo's and go back to the exact same place and take the photo again. Maybe you've found a scene that you want to take all 4 seasons at you would be able to go back to the same place and do that.
How do I geotag my photographs? Well there are many ways to do it. Once your in the map module you could simply click, drag and drop your photo onto the google map where you took the photo. If your like me you don't always know the exact location on a map you could use a GPS device or your cell phone with the correct app to create GPX tracks. Then you could import the track (which is like a digital breadcrumb trail) and then you could auto tag your photo's and they will appear on the google map with all the right coordinates on them. You do have to be careful and make sure your camera and your GPS device or phone are at the same time or they might not sync into the correct spot on the map.
Here is a quick video on how to use the Map Module in Lightroom : https://www.youtube.com/watch?v=nH6sg5Yzhwg