So I only just got my first character up to level 10 last night on Ultros. In case anyone is curious, I'm playing as a Mi'qote named Yuri Paw (creative I know, right?) as a Thaumaturge. I've basically been following the quests wherever they take me and having fun playing the game, but I still feel very unfamiliar with what the game has to offer.
I've been browsing some of these guide sites in the OP, but one thing I'm not finding directly is what kind of quests of special abilities become available when? For instance, I have no idea still when I gain access to a mount, or the ability to change jobs, or even what all the jobs in the game are. I know there's a summoner class, but only because I've seen people use avatars in the game...yet I don't even know what all jobs available are.
Maybe I'm thinking too much that this game is like FFXI, but the thing is I just don't know...like that game had advanced jobs at level 30 you could go after, is there even something similar in this game? I kinda miss the simplicity of the interface that that game had with access that kind of information. You go to your mog house, and under change jobs, you know there's at least X number of jobs you have yet to unlock because there were slots with ??? there.
I believe you get the chance to unlock job changing at level 10. I think you need to do your level 10 job quest first, though. As far as advanced jobs, you gain the access to unlock these at level 30 through your job quests. Once you complete the quest, you get a pearl or crystal that you can equip on your character that lets you change to the advanced job.
All you need to do to change jobs is fine the job's guild, talk to the NPC with the quest icon above their head, and they will let you into the guild. They will give you the starting weapon for that class, you equip it, bam, you're that job.
For the mount, once you get into a Grand Company (you get to choose from the three large cities), you can get the quest to get the Chocobo. You will need to do things that give you Grand Company seals (you get them from fates, from supply and provisioning missions, and Grand Company hunting logs). Once you have 2,000 seals, you can get a Chocobo.
CLARIFICATION EDIT: You join a Grand Company by going through the main story. Those quests will walk you through joining one.
You can see all of the base level jobs on your character menu (Shortcut: push C on the keyboard). There will be a tab in this menu that shows you the available starting jobs.
You get Summoner by leveling Arcanist to 30 and Thaumaturge to 15, then doing the level 30 Arcanist mission acquired at the ARC guild.
YET ANOTHER EDIT:
http://xivdb.com/ is a good place for information. Go to Skills, your battlecraft class, and it will show you all of the advanced jobs underneath the starting jobs. This is also a great site to find exactly where hunting log mobs are.