I have a video and the author has two to watch this time. To help further understand, here is an INTERACTIVE FIGURE. To help with the units, look at SCREENCAST UNITS, and to help with free fall and non-free fall scenarios, try SCREENCAST SKYDIVER.
Source: (C) 2016, Pearson
Source: (c) 2016, Pearson
Source: (c) 2016, Pearson