The first partner drill is focused on making sure we get our elbows to the mat prior to the arm bar attempt by the person attempting the arm bar. This drill will get the beginner used to getting their back the the mat and sucking in their elbow in tight on the arm that is being attacked.
The second drill focuses on the details of escaping the arm bar while you are being attacked and the attacker is stepping their legs over the head. The key here is that after we block the opponents attempt to put the leg in front of the head, we make sure we get our back on top of the leg of the leg of the person attacking the arm bar. Once we escape the arm bar we can turn into the guard and work to escape the guard rather than the mounted armbar we had been in previously.