Meta is just a key-value you can tack on to an individual post. Plugins use it to add additional information to a post instead of defining a separate database table. There is some info about the meta db tables here: code.tutsplus.com/tutorials/unders...
EDIT: Also, it has nothing to do with META html tags. To modify those, you just need to change whichever PHP template file contains the head tags. Just use PHP to set them to whatever you need. You could technically pull from post or user database meta data to populate the html meta tags. That's a method. Or use a hook to print them in wp_head().
Meta is just a key-value you can tack on to an individual post. Plugins use it to add additional information to a post instead of defining a separate database table. There is some info about the meta db tables here: code.tutsplus.com/tutorials/unders...
EDIT: Also, it has nothing to do with META html tags. To modify those, you just need to change whichever PHP template file contains the head tags. Just use PHP to set them to whatever you need. You could technically pull from post or user database meta data to populate the html meta tags. That's a method. Or use a hook to print them in wp_head().
And here is info on interacting with metadata via the API. torquemag.io/2015/07/working-with-...