An email newsletter is something that you receive in your email that gives you information about a company or service. Sometimes you subscribe to it (I subscribe to Hungry Girl - really) and sometimes it arrives without your permission (and probably ends up in your Junk Mail folder). It usually has a lot of graphics, and in the business, we call it HTML mail. The leader in the industry on this is "Constant Contact".
The advantage to an email letter is that it puts your message right in front of people, assuming that it arrives in their "in" box. With a blog, your viewers need to go onto the web to read it, or they can read it through some type of reader.
The disadvantage to an email newsletter is that it is limited to the people in your email list. A blog, like this one on Google Blogger, is available to the world. Every word is indexed in Google and can be searched. If what you are saying interests the world, they will find you.
If you would like to get personal on-site software training in Adobe Photoshop, Illustrator or Dreamweaver in the greater Phoenix, Arizona area, please contact me.