What did the commisioning of the preaching of crusades involve?

I was reading about [St. Bernard of Clairvaux](http://www.newadvent.org/cathen/02498d.htm) , and this appears: > The pope commissioned Bernard to preach a new Crusade A similar phrase appear in the respective [Wikipedia](https://en.wikipedia.org/wiki/Bernard_of_Clairvaux) article. I get what it means to "preach a Crusade" (call Christians in favour of it and to join if possible). The [article](http://www.newadvent.org/cathen/04543c.htm) in the Catholic Encyclopedia about Crusades states: >All crusades were announced by preaching. But, what did the **commissioning** of such preaching by the Pope involved? What were the responsibilities? Could someone provide a reference for this? Maybe a papal document related to such commissioning?