The second MSG was launched on 21 December 2005 on the same type of launcher as its predecessor - a standard Ariane 5 - from the same launch site - Kourou in French Guiana. It is currently in the same fixed section of orbital space as MSG-1 in geostationary orbit, close to where the equator meets the Greenwich meridian.
The reason for the duplication is simply to guarantee continuity of service in case of satellite failure. Weather satellites have become so crucial a part of our daily life that any long gap in service coverage has become inconceivable.