Apple, naturally, would prefer you buy their webhosting service .mac (or whatever its called now). It's (probably) over priced if you dont need it's other features or already have it.
When youre done designing, click the file menu. Then there is publish to .mac (or whatever) and publish to folder.
If you have the other webhosting (that omega is talking about), youre going to want to hit publish to folder. Then upload the contents of that folder to your host using FTP software (such as cyberduck).
You could also poke around in the export menu. Im not sure whats in there (don't have the program with me)