I know about Wordpress CMS. But, I don’t know how Wordpress.com works.
I imagine that very big data in the database server.
Does it generate a new database name for each wordpress.com site ?
Or, just a new table ?
How come the page loads just in seconds ?
Are there any good books about web administrating ?
Each Wordpress site will have a single database containing multiple tables. The size of the database depends entirely on how much content has been entered into it; no content - small database, lots of content - bigger database.
The speed of Wordpress is down the the way it was designed, the technology used (PHP, MySQL), and the hardware it’s running on. It’s worth noting that when you visit a Wordpress site, you are not downloading the whole database, just those elements within the database that you need for the page you are looking at.
wordpress.com is running the same code as you can download from wordpress.org with the multisite option turned on. If you want to see for yourself how wordpress.com works then you can always download a copy of wordpress and set up your own equivalent.