# connect as root to the MySQL server
# all this is saying connect as user 'root' with password i am going to provide.
# you will be prompted for password after you press enter.
mysql -u root -p

# Once you are connected you will be presented with the following prompt
mysql>

# if you want to learn type in
mysql> /h

# otherwise do the following to create a username and password and table.

# create database
CREATE DATABASE testdb;
# create user 'testuser' which can only connect from localhost with password 'changeme'
CREATE USER 'testuser'@localhost IDENTIFIED BY 'changeme';
# you give it permission to create and edit all table in the testdb
GRANT ALL PRIVILEGES ON testdb.* TO 'testuser'@localhost;
# you exit mysql
exit