I don't recall exactly how to unlock guildhests exactly, but I *think* it was by undertaking a levequest from your starting city-state, which leads you to a nearby town in a field map (Bentbranch Meadows in Central Shroud if you're from Gridania, Horizon in Western Thanalan if you're from Ul'dah, not a clue about Limsa Lominsa), which then has an NPC in there that unlocks guildhests. They are sort of a mini duty of sorts, far shorter than a dungeon, lasting between something like 30 seconds for the shortest ones, to maybe five minutes for the longest. In retrospect, I don't think guildhests give company seals. I believe that only the guildhest roulette does. The guildhest roulette is unlocked after completing either the first, or the first two guildhests, I forget exactly.

I apologize for the unclear information. Would be easier for me to confirm some things if Aether was not down. x_x