Most of your answers are in http://wordpress.org/docs/
Lets take one step at a time. The front page of WordPress is something like a normal web page. It is written in xhtml. Simple. Included in it are a lot of php functions. So that makes it a php file. Those functions call data. You are quite right. That data is stored in a database. The particular type of database is called mysql. So if you wanted to change some items on the *home page* you could add something there in xhtml. If it was a change to the way the data was called you would edit one of the php functions. If you were a guru you could edit mysql itself. Either directly or through a graphical interface like phpadmin. So the full answer is – it depends on what ypu want to change.
Now here is the good news. None of that is strictly necessary at all. What you prolly care about is the way your stuff looks . Again you are right. It is styled using CSS. That is all in one file called wp-layout.css. Each *bit*
of the front page is labelled if you like – with a tag. How that tag looks is set out in the CSS. So to change anything you need to do 2 things. Identify what you want to change. Then find the appropriate selector in CSS and change it. You may do that in any text editor you choose. Good luck. And Welcome to WordPress.
