As of now (with little experience in the public relations field), I think of PR as a type of promoting.  PR can be done by either one person (a PR representative) or a PR committee or team.  This person or committee can be used to promote anything from a huge organization to one person (such as someone famous or running for a political office).  The job of PR reps is to first of all, get the word out about their organization or person, and to then convince the public to have a positive view on who or what they are doing PR for. 

I am pretty sure PR reps also deal with conflict between who they work for and the public.  When the public sees something negatively, the PR rep may try to lessen that negativity by giving speeches or making statements about the good in their product.

As I already mentioned, I have little experience in the PR field so this is just about all I know.  Obviously by the end of the semester, I am hoping to know a whole lot more!