Dear Student,
In response to the first part of your query, product concept of marketing believes that consumers favour, superior quality products and hence, profits can be maximised by increasing the quality of the product. So the focus of the business is on improving the quality of the product, adding new features, etc.
On the other hand, selling concept of marketing says that good for which a lot of promotional activities are undertaken in the form of advertising, publicity, gets sold in the market easily.
In response to the second part of your question, publicity is an unpaid and impartial way to generate awareness about a particular among consumers. It can be positive or negative, since it gets generated from an impartial source.
Keep Posting!!