Under the basic subscription you can have 6 characters, total, spread across as many servers as you like. You can have all 6 on one server, or 1 on six different servers. However you like. After you have 6 characters, if you want a new one you have to delete an old one. If you want more than 6 characters available to you, you need to buy a second account or station pass (but that's only cost-effective if you play other SOE games).
If you start a character you don't like, just delete it and start a new one. You can have /up to/ 6 at a time, but there's no limit on how many different characters you can create within that 6 slot limit.
Edited, Apr 19th 2007 10:19am by Stugein