To login, simply use the UserName/Password you provided during the setup process.

If you did a SQL dump, then simply login with admin/admin (case sensitive), and be sure to change your login information!

Also remember change file permissions on mainfile.php back to read-only (0444 unix), and be sure to delete the entire /_install folder from your server for security reasons.

REMEMBER:
To be able to save your configuration data, you need to make all /cache folders world writable (0777), and any files in them (0666).