Blogs are like online diaries or journals - entries in the blog are displayed in date order (with the most recent entries first) so they are an ideal way to keep people up to date with your activities.
The calendar on the right allows visitors to easily look at older entries.
Visitors can also use the email notification or RSS feed on the right to be alerted every time that you add a new entry.
You can add entries to the blog in the same way that you create web pages (so you don't have to learn anything new in order to be able to run a blog on your site).
You can include formatted text, pictures and links.