In theory, categories are a natural and wonderful way to display information. In practice, however, I completely avoid BC's implementation of categories. It is almost worthless. It has limited output capabilities, and no sorting capabilities.
As if that wasn't enough, the Blog module doesn't have the ability to list all by category. It's somehow missing that feature. While there are workarounds for this, most aren't worth the time. Here are the couple that I recommend:
- If your blog is new, without a bunch of previous posts, you could use Web Apps instead of the Blog module.
- You could create multiple blogs, one for each category, and then list those blogs out on the page.