You can access MySQL from command line by typing in a terminal:
mysql -u [username] -p [password]
[username] is the user you setup during install and
[password] is the password for that user. If the password has special characters (such as $ or !) then you can leave the -p blank and it will prompt you for the password.
As far as phpMyAdmin, you need to edit the default Apache2 conf (usually located at /etc/apache2/apache2.conf or /etc/apache2/apache.conf). Make a backup (
cp /etc/apache2/apache2.conf /etc/apache2/apache2.conf.bak) add these lines to the end of apache2.conf:
# Include phpmyadmin
Save the file. Then, restart Apache2 with:
service apache2 restart
Now, you should be able to access phpMyAdmin by typing
http://localhost/phpmyadmin in the address bar of your browser. I hope this helps.