http://download.geonames.org/export/dump/

here you can get all the countries geojson files..

check it out..

and there are lots of tutorials available to do the task you requested...

http://www.schneidy.com/Tutorials/MapsTutorial.html

http://techslides.com/d3-world-maps-tooltips-zooming-and-queue/

apart from these you need to search and find tutorial to learn much more concepts...

These two are the basic tutorials to…