Yes, you have to complete a certain main story quest in order to take on levequest - the specific quest is called 'Spirithold Broken', it's the same quest that also unlocks the Inn. Once you've completed this quest, speak to Gontrant, the elezen at the leve counter in the Adventurer's Guild and you'll be given another quest to speak to Tiereny at Bentbranch Meadows. She'll give you a trial guildleve to complete, and once that is done, guildleves will be unlocked completely. Just remember you have to undertake a trial leve at every levemete you want to do leves from, but the extra exp and gil is always good.