Pic 1.
Think of it this way. In straight and level flight, lift must be constant. So at any point on the drag curve, the lift required is the same. Therefore the point where the drag curve is a minimum is the most efficient, as it produces the least drag, but still gives the same lift as other points on the curve. This then corresponds to the points you have listed under the pic.
Pic 2.
Endurance is related to how much fuel you burn. The more you burn, the faster you run out! Bob puts it very simply in his book. Power is a rate, and you can think of it as a rate of burning fuel. The less power you use, the less the rpm's you use, the less rpms you use, the less fuel the engine is using per minute i.e. it is taking a smaller bite of fuel (lower rpm). Therefore, for maximum endurance, you would operate at the least power required, point x on the graph.
Alternatively a simple way of looking at it is like peddling a bike. The faster you pedal, the more energy (fuel) you use so your become tired (run out of fuel) more quickly. The slower you have to pedal, the longer it will take for you to become tired.
Pic 3.
Not sure what you want to know here, but the answers would be the same as pic 1. The highest L/D point will occur when the airframe is operating at its most efficient angle of attack i.e. The least total drag.
Pic 4.
Not sure what you wan to know here either? But CL will increase all the way upto the stalling angle, and then drop off as the stalling aoa is exceeded. I like to think of the CL as how efficiently the aerofoil can use the energy of the airflow to produce lift. At high angles of attack, the wings can "manipulate" the airflow more to produce the required lift (until the critical angle is exceeded)
Hope that helps, these are just the pointers I use myself to understand how the graphs work. Someone else might be able to help you more if its not sufficient for your needs.
