Why you should have a Blog on your website
In short, a Blog is an article written on subjects your website visitors might find helpful. You should write articles on subjects you have a lot of knowledge on. Once you have these articles on your website, other websites might link to yours on the subjects that you have posted on.
Another reason is Google and other search engines, LOVE blogs. This will enable you to have fresh content on your site, without changing much on your website. Fresh content will always rank higher on Google and other search engines because it is newer content that they might not have indexed yet. Older websites that do not update, will rank lower!
There are a lot of software packages out there that help you write these articles, such as WordPress or Joomla. These software packages can be extremely helpful and make writing a blog easy to do. If you know how to use Microsoft Word, then you pretty much know how to use the backends of WordPress and Joomla.
You should try to write at least 3-4 articles a month to obtain good SEO listings but try to write a minimum of 1 article a month. You can also write articles all at once, and not publish them to the web until you are ready. Good example of this would be write up Christmas articles in July, then tell your software to publish them in December. This way you can write up all of your articles at once, then publish them throughout the year.
Remember fresh content is always good!