How do I start? I have never did a blog before. I have a nice informational site that's getting very little traffic, so I figured I would turn it into a blog with fresh content updated weekly. Maybe put google adwords on it.
There's nothing really special about having a blog compared to simply putting fresh info up on your existing site on a regular basis. There's no special magic that comes from having a blog in terms of rankings. Regularly updated content is the key.
If you're looking for blog software though, take a look at MovableType, WordPress, or Blogger. Those are some of the more popular software/services for bloggers.
One of the biggest issues will be directing your existing traffic to your new site setup. To be honest I would tend to go down a slightly different path. I would retain the main info site, and have the blog as a site section. What I would perhaps do is to continue to update the main site as often as possible. And add the importaint stuff to your blog area. That way the blog has only the very compelling content and that can be syndicated via xml/rss. The blog could hold a snipped with a link to the main article on your existing site.
This means that all info is posted on your info site, where as only the content that you class as importaint makes it into the blog.