Rodent Regatta

Ok, I’m confused:

1. There’s a CSS style sheet that Movable Type uses to format these entries.
2. Using MT’s text entry box, I have some latitude to enter some HTML tags. If I don’t choose the correct ones, I make it impossible to validate this weblog. Right?
3. If I use Zempt to do something, it chooses a particular way to tag the text.
4. How do I know/determine which way is ”right?” Both of them ”work.”

Perhaps an example would help. There are two ways to center something inside a blockquote. The first way is to tag the text with [center] [/center].

The second ways is the way Zempt does it with [div align=”center”] [/div].

How do I learn/know/determine which of these is the ”proper,” well-formed way to do things? A similar question arises with [bold] vs. [strong] and [i] vs. [em].

Help!