SQL Developer is just a client tool. It requires a database to be used. If you don't have a database, then we can't help you. Do you have a database, or access to a database?
If not, try out our self-contained virtual machine that includes a database, SQL Developer, and some self-guided hands-on-labs:
Edited by: Jeff Smith SQLDev PM on Oct 27, 2012 9:10 AM