I am not sure if I am using right name of "Categories" since I could not find what I am lookig for in plugins.
What I want is: I have a multisite with single domain, when people register a blog on my page I want them to specify what category their blog belongs to. And on the front page of my domain, I want to have a listing of all registered blogs by category. Same thing what they have on this page on left hand side:
http://geocitiessites.com/
Thank for your help
Just to clarify, I might have used wording that could have confused readers.
I am not talking about "category" that you can specify when wring a blog, so each user can have each blog they write in a different category.
What I am talking about is people that register on my page to get a "site" I would like to have them categorize their site.
Example, I will have cars related site.
This will allow individual sites to be categorized and listed like on the page example given previously.