I’m not sure why you’d be in phpMyAdmin when instaling phpBB, it’ll make the tables for you, you just have to provide it with:
you should be able to set those up in your control panel before you try to install the phpBB software, from the Goodies/MySQL page. Create a database, add a hostname, add a user and pass, then you’ll have to wait for a mysterious amount of time for the hostname to kick in. After the dust has settled you should be able to follow the quick install instructions that come with the phpBB.
Now that I think about it, if you’re in phpMyAdmin, that means you’ve already set up the host/db/user/pass so just plug that into the config file, upload, run install