A press release is just a marketing document. You can search for press releases that other companies have done and then simplyi use their format to write your own.
Your follow-up question is likely to be, how do I distribute a press release....
There are services (for a fee) that will do this, as will marketing companies. You can also look up the webmaster or editor addresses on most news sites and see who the contact is. You can then email or send the release to those people. As a note, editors get hundreds if not thousands of releases, so if yours is not unique or directly related to what they cover, then they are unlikely to do anything with it.