This is how you do it,
In order to achieve this, there are various ways to obtain rank 22, there are Guildleves, Behest, and you can also grind on mobs.Firstly, you need to be at rank 22 of any class to join a grand company
Few tips for new players, Do main story quest from your respective home nation to obtain Retainers and it is also needed in few class quests that will be coming up later on at rank 20.
This is the lists of the Main Scenario Quest, i'd reccomend doing just so you will have no issue advancing in any other quests.
Ul'dah's Plotline :
Flowers For All
Courts In the Sand (rank 1 requirements)
Golden Sacrifices (rank 8 requirements)
Calamity Cometh (rank 13 requirements)
Gridania's Plotline :
Sundered Skies
Souls Gone Wild (rank 1 requirements)
Whispers In the Wood (rank 8 requirements)
Beckons of the Elementals (rank 13 requirements)
Limsa Lominsa's Plotline :
Shapeless Melody
Treasures of the Main (rank 1 requirements)
Legends Adrift (rank 8 requirements)
Never the Twain shall Meet (rank 13 requirements)[/I]
**Every home nation has their own story up until rank 13 quest then everyone will be gathered up at Ul'dah under this quest Fade to White (rank 20 requirements), and will advance the main scenario along with everybody else. *finish Fade to White so you are able to advance in most sidequests or class quests.*
There are 3 Grand Companies total as of now, one from each nation, you can join all of them up til Recruit rank. These are the list of quests you need to do to get Recruit rank.Secondly, after you have done getting up to rank 22, learning the game mechanics and what not, it is time to join the Grand Companies.
Career Opportunities for Uldah's Grand Company,The Immortal Flames
The Price of Integrity for Limsa's Grand Company, The Maelstorm
Breaking the Seals for Gridania's Grand Company, The Adder's Nest