As far as I know, there is no technical difference between "ultranationalism" and just plain nationalism.  The former is just a more extreme version of the latter.

Nationalism is the idea that there is something unique and superior about your ethnic group or your nationality.  As this gets to be more extreme, it starts to include a violent hatred of another group or groups.  So Nazism would be an example of this.

It usually arises in a society when the society has fallen on hard times.  People look for scapegoats and often pick a group of "foreign" people to blame for their problems.

This is important because it can lead to attempts at ethnic cleansing or even genocide.

Ultra-nationalism help please? Thank you very much! What is Ultra-nationalism and how does it emerge in a society? What is the importance of this issue? Please explain in detail.  

Ultra-nationalism is an overtly strong identification to a society.

"Often, it is the belief that an ethnic group has a right to statehood, or that citizenship in a state should be limited to one ethnic group. It can also include the belief that the state is of primary importance, or the belief that one state is naturally superior to all other states."

Ultra-nationalism is sometimes a response to an event.  During World War II when the US fought the Japanese we rounded up US citizens, of Japanese desent, and placed them in internment camps.  This can be seen as a form of ultra-nationalism. 

Ultra-nationalism is important becasue it can shapes society and governments.  It may lead to war, genocide and other atrocities.

Ultra-nationalism help please? Thank you very much! What is Ultra-nationalism and how does it emerge in a society? What is the importance of this issue? Please explain in detail.  

Nationalism is the devotion to a person's country and ideals. Ultra-nationalism is this devotion to a greater degree. Now as for how it arises, there is no single cause and easy explanations are not possible. However, if I had to take an educated guess, I would say that it probably starts with a powerful group of people who run a country and start creating an ideology that basically states that they are the best and that other countries are lesser. In time, there will be less cooperation with other nations and thoughts of international interest will be diminished. The problems of ultra-nationalism are great. First of all, it may cause war, if this ultra-nationalism is not checked.