Correction: I'm holding down the T key, while using Polystrips, to use the Polystrips Tweak tool. (Not the regular, stand-alone Tweak tool.) The video says to hold T and you can tweak things while using Polystrips. Nothing happens when I hit the T key. Anyone know what I'm missing? I'm sure that I'm just missing some step.
Answer found! Carter2422 answers another person with this problem. You have to apply transformations (transform, rotation, scale) on both source and target. I had a 90 degree rotation on my source object. I applied that, and the T hotkey for Polystrips Tweak will now work.