On a fresh install there is already a default user, and that's root. If you want to add more users, you have to login to mysql with root first. Instead of just typing mysql at the \mysql\bin directory command prompt, type:

mysql -u root myqsql

This will connect you to the mysql server as root. Also, the user 'root' doesn't have a password on a fresh installed so once you've successfully connected using the above, you should change root's password:

update user set password=password('your_password') where user='root';

Then you can add all the users you like. Check the manual for this information as it is clearly detailed on what you need to do to create new users. Cheers.