Questions - blog functionality for the clueless
 

Under the assumption there are no stupid questions...
Yesterday 1/26 I signed up and by following a link that had tabs for write, design, and two others I can't recall, I was able to write and publish an entry to my blog.
Today I signed in and see yesterday's blog but no place to write today's. there's a comments section but I don't think that's it.

Also - what is a tag? What is a category?
I added a theme but I wonder if there's a link somewhere that expalins all this? I read some posts that were helpful but no place that really explains where and how to design the blog page, add links, pictures, etc.

Clueless I guess!