Localhost Newbie Question

[shirotensaki]

I started building a site with php using xampp (for mysql and apache). I tested it using a database i created on the xampp php my admin. To connect to it i had to use localhost as a server which made complete sense to me cuz the database was on my computer. Now i wanted to progress a little and build the database online for when i bring my server online. I created the database, and wrote a few tables, i could then log on and admin and edit them no problem. Only problem is now i can't connect to it thru php. Now my real question is why is the hostname on the server for Zymic localhost when it's online and not on my local disk and how is php supposed to know where the database is if i never gave it an address for the site. How come the hostname is localhost no matter where the DB is located? Maybe if i understand that i can understand why my database won't connect.