What a question??? Are you serious? Promotion is advertising your site and getting it know. Public relations is anything dealing with the public, customer issues, etc..
Are you for real? There is this thing called Google search engine, type in your keyword and with a hit of one button you will find your answers. Welcome to the millennium!
How to communicate to the public about the company, products in the form of press conference, event marketing, press release or publicity. www. InternetAd.biz