When you use Blogger in draft, you'll see an option below the post editor to "add location". If you know the exact location, you can simply enter the address, city, or zip code; if you're blogging about the view from the top of a mountain you just hiked or don't have a precise location, you can browse the map or turn on satellite mode and put a marker at the right spot (and the reverse geocoder will label the location for you). The geotag will appear below your published post as a link, which will open up Google Maps. The location will also be included in your blog's RSS and Atom feeds using
GeoRSS.