Please read the docs. It was too explained in detail here on the list some month ago.
Also check the comp.protocols.dns.bind newsgroup (mirrored as the ISC BIND mailing list). Googling that group should turn up lots of useful information. You'll also find lots of useful links at the ISC BIND web page:
<http://www.isc.org/index.pl?/sw/bind/>
Did you read the bind documentation? DNS is a fundamental service and you should not play around with it.
Playing around is how you learn, and in this case you can't do much damage from a bad configuration (like you could with an open sendmail relay).
Another thing to note is that zone files are full of abbreviations designed to make them easy to type. But those abbreviations can be confusing. For example, "@", ORIGIN, and omission of various record parts are useful shorthand for experts. When illustrating the syntax to newcomers, use full records and then show how the shorthand makes things easier to type.
