Ok, ok... enough chatter. This is how you create your very own, personal blog:
First off, go to
Preferences (at the top of the board) and click on
update profile. You will be presented with a screen that looks like this:

Now, click in where it says
My Blog and go to next screen, that should look an awful lot like this:

Here you can choose a name as well as to add a description to your journal (and write a bit about yourself... if you feel like it). See all the privacy options at the button? Choose whichever suits your needs better, but don't worry... you can edit all of this at any time.
Once you are satisfied with your blog, click on
save changes and it will be created! Easy, isn't it?
Your blog is almost ready now! But wait... where do I choose to have categories? Well, that's easy (although, probably the only step on this that's not as intuitive as it could be). To accomplish that goal, you simply need to click on
change blog settings and scroll to the bottom of the thing, where you will find this:

Now that you are all set, click on
post a new blog entry and let the brainstorm begin!