Its documented on the MySQL site.
MySQL ALWAYS COMES WITH THE 'root' SuperUser userid configured and the password in not set.
What makes you thnk you can just invent a userid????
So login using
Username = root
Password = blank, just leave it empty
Then set a password on all 3 root userid, best to make them all the same. Yes there are 3
root@localhost
root@127.0.0.1root@::1