Its telling you what tabs you have to click in the phpBB3 in order to add the meta tags module(page).
Go to the ACP, then click on the system tab on the top tab bar.
Then click the Administration control panel link on the bottom left hand side of the screen.
You should now be shown a list of all the modules in your acp (General, Users, User permissions etc.)
It's telling you to click the link which says General, then click server configuration, then click the drop down box in the bottom right of the screen and click meta tag module or whatever it's called.
Then click add mod.
Make sure it's enabled, and it should then appear on your ACP's homepage
In future, it might be better to first ask the mod author for help, as they'll understand their install instructions
