Welcome to Eorzea! (the full version )

Main scenario quests run in a certain line (identified by a meteor icon), and usually the npc you need to get the next quest in the scenario from is the same one you completed the previous quest with (if not, the relevant npc will be standing nearby). So if you lose track of where to go in the story, open your Journal and have a look at the last quest you completed and find who it was you completed it with, and then simply track that person down (the Journal will mention the zone name of where that person is if nothing else).

Anyway, I'm glad you were able to figure it out on your own. Get ready for your first Primal trial which is coming up.