Hi Christyan! A blog is basically a little journal where you talk about pretty much anything. Could be forum-related or something about your life; it's your personal space to to write down whatever you'd like so long as it's appropriate, of course. In order to be able to create blogs you'll need either 2,000 posts, be a gold tier supporter (donate $15.00 or more to the forum), or become a staff member.
Hope this helps! [: