Can I scrub the timeline in AE (CS4)?

Hi guys.
Sorry to post two back-to-back questions on the same forum. I'm completely new to After Effects, and (as I'm sure you know) it's a whopper of a program. I've watched many (many!) of the Lynda.com tutorials, but it was a lot to absorb. I'm wondering if I can click and drag (i.e. "scrub") the timeline. It seems I can't; rather, I have to click along the top of the timeline for an updated frame in the viewer window (if it's called "viewer"). This makes it pretty complicated in making adjustments to animations. Is there somewhere I can turn on scrubbing?
Thanks again!
Vic