Ah! This stumped me too. It's there in the instructions, but easy to assume we can drag the layers in the timeline like After Effects.
I guess that'd be my feature request: It seems like the Elements box and the Timeline box could be combined (but I'm new).
Maybe for now, just a warning in the tutorial would help. (e.g. "Note that you need to do this in the ELEMENTS panel, not the Timeline panel...")