Priority_Queue..

I was trying to implement some data structures using priority queues just then i found something like

priority_queue< pair < int, int>, vector< pair< int, int> >, greater< pair< int, int> > >p

and

priority_queue< pair< int,pair< int,int> >,vector< pair< int,pair< int,int> > >,greater< pair< int,pair< int,int> > > > p ;

can someone explain me what does these structures actually do or how do they store the data in them.

and how are they different from simple structures like

priority_queue< pair< int,pair< int,int>>>

thnx..