If you wanna see another example...
When x is negative and gets closer to about .75, the slope is positive, but is getting SMALLER (which is why the yellow graph shows a decreasing answer as x approaches .75).
Once x hits .75, the slope is 0 and begins to decrease, but then starts to level out again as x gets closer to 0 (which is why from .75 to roughly 0, the yellow graph decreases, then increases).
After that, the slope does nothing but increase, as evident by the yellow graph.
I forgot to mention earlier: Third derivative graphs determine concavity of the first equation (either concave up or down, which is the "U" or upside down "U" shape the graph takes)
If you want to test these out on your computer, you can use the program I used to make these graphs (WinPlot, it's free):
http://math.exeter.edu/rparris/winplot.html
Once you load it, hit F2 to load up a blank graph, then F1 to add equations to it. You can change the zoom and everything to give you a better idea of how these graphs work together.