Ok in all honesty they did give some information on what grand companies are, ill run through it again for those who cant see past the lore.

Grand Companies will be a new allegience players can join
It does not matter where you are born/come from
they will have various missions for players to do
they will have content/quests/missions that varies from battle, to gathering, and crafting
you can try out different companies early on.
Eventually, to progress you will have to pick one company
You will get a rank in the company
Ranking up in the company will provide items/gear at high levels, and unlock harder content.


So yeah there is info that we didnt really have there, but i still say they should try to put more of this type of info in game in some form. Its good stuff to have, allow the option to be given to all players, not just those who read the lodestone.