Its really just 2 characteristics I guess you could say that relate to flying at the maximum CL.
If we consider the lift equation for a second you will see that lift generated in flight depends on a number of factors:
L=CL x 1/2pV2 x S
Since Lift must always equal Weight in straight and Level flight, it follows, that the value of Lift must be constant with respect to weight. Consider the above factors that make up Lift, if we increase one factor, we must reduce another in order for the lift value to remain constant.
The 2 main things that the pilot has control of is generally CL, which varies with the angle of attack, and V2, which we change by altering the power setting. We can also change S but we shall ignore that for now to avoid considering too many factors.
As a result, if we increase CL i.e. angle of attack, we must reduce our airspeed V2, otherwise the value of Lift will increase and we will start to climb. Therefor by increasing CL, we must reduce V2, and if we reduce the CL, we must increase V2. This is all done to ensure the value of L remains constant.
Hence to answer question 14, when CL is at a maximum, the speed V2 must be at a minimum to ensure Lift remains constant. This speed also represents the stalling speed, to question 19, since the stall speed is the slowest possible speed, V2, that can be used to maintain Straight and Level flight. If we fly at the slowest possible speed, we must have a high CL value for the Lift equation to remain in balance.
Figure 7.2 on page 7.2 pretty much sums up the relationship I have just described above.
Hope that helps.
