To create an typical, "ordinary" MySQL account with full access to one database:
mysql> GRANT ALL on databasename.* TO 'typicaluser'@'localhost' IDENTIFIED BY 'thispassword' REQUIRE SSL;
Note that the "REQUIRE SSL" is optional (and requires that SSL be first setup, which it is not by default). "localhost" may be replaced by an IP address, or by a '%' to permit access from anywhere. The '*' may be replaced by a specific table name, to grant access to only one table.
To create a root / superuser with full privileges to everything and all databases use one of these methods:
mysql> GRANT ALL PRIVILEGES ON *.* TO 'privileged'@'220.127.116.11' REQUIRE SSL WITH GRANT OPTION;
mysql> GRANT SUPER ON *.* TO user@'localhost' IDENTIFIED BY 'password';
To see any given user's privileges:
show grants for user@localhost;
Theoretically one can rescind any of those grants with a REVOKE statement. Follow any and all of this privilege modification stuff by:
mysql> FLUSH PRIVILEGES;
And finally, to remove a user:
mysql> DROP USER 'privileged'@'18.104.22.168';
Note that many (including myself in the past) would say that deleting the user record from the mysql.user table is how one goes about this. In fact, if you do this, and then click the "Privileges" tab in phpmyadmin, you will probably find that user still listed. Use "DROP USER" instead, to delete all mention of this user from all privilege tables.