Press Releases are sort of the old way of doing business and have never worked for me. That said I still submit a few press releases every 6 months just because you never know and it is always good to have another site linking to your store.
First you need to write a press release. Here is a great article on Wiki How on how to write one.
There are a gazillion places you can submit your press release. Here are the best ones:
Personally I would never pay to submit a press release (all the ones mentioned above are free or have free options). If you had to pick where to spend you time you are better off contacting bloggers/newspapers directly and telling them about your product.
Tags: press