Don't worry about the terms. One thing SBI! does very well is provide little question marks by almost every explanation and they explain every term you need to know along the way.
What you choose to blog about is up to you, but if you are going to use Site Build It!, they are going to suggest you keep your blog on topic with what your site will be about. No sense in building a site on fashion for example but then creating your blog on another subject. Site Build It!'s blog feature is tied in with your site so you really want to make the two match.
If you want to create a separate blog on photography you can always sign up with
www.blogger.com or
www.wordpress.com and do that completely separate from your Site Build It! site.