I just started and I'm so lost - Help!

[Bixby]

Right about the leveling. Each job is a piece of equipment (soul crystal) that you wear on its base class. When you are a bard, you are a level X archer wearing a bard soul stone. You don't technically level Bard, you just level Archer (edit: which happens regardless of whether you currently have the Bard soul crystal equipped or not).

Each job also has two classes that it can pull cross-class skills from. For Bard, that's Pugilist and Lancer. For each job, one of those two classes is also required to be at 15 to open up the quest that gets you the soul crystal (Pugilist for Bard).

In the end, once you've unlocked the job, the "sub" classes are nothing more than cross-class skills. You don't adapt anything else from Pugilist or Lancer game play, you don't get stats or anything from them. Just cross-class skills.

Not everything opens up through the main story. Here's a nice list of when and how all sorts of features (including dungeons and trials) get unlocked. Guildhests are a little unique in that once you unlock Guildhests at all, they all just unlock by level (2 hests every 5 levels up until 40).