In the Search tab you can look up places by their geographic names using public geoname services GeoNames and OpenStreetMap. You just type in a name of a place (city, monument, hotel, …) into the input field at the top and click on Search button. In the result list below you will get something like this:
Obviously Paris does not only exist in France. So if you were looking for the capital of France you can either scroll down the list until you find an entry that undoubtedly belongs to there like Arc de Triomphe and click on it or specify your search a little bit more precise like Paris, Arc de Triomphe or Paris, France. Once you click on an entry in the list the map will become centered to that place and you can now zoom in with the zoom-in button (second from the left below the map). Using this example with GeoNames you will notice that you still get a lot of results and even two labeled only Arc de Triomphe, the second one a street a few hundred meters away from the arch. With OpenStreetMap you get only one result. You got to play a bit with the different services in different regions, with more or less precise search terms and then you will get an idea about how to best conduct your searches.
For the buttons right above the result list refer to their tooltips! The context menu on search result entries offers:
Copy Coordinates which you can paste later to one or more images in the image list under the map
Move Selected Images To This Position which is basically the same but more straightforward provided you have the images already loaded into the geolocation editor
Remove From Results List which is particular useful in conjunction with the Keep-the-results-of-old-searches-… button above the results list.