I didn't read you document really, but I can understand why you are confused. But it is a very simple concept really. Let me explain.
Triggering: This means making a circuit active. Making a circuit active means allowing the circuit to take input and give output. Like for example supposed we have a flip-flop. When the circuit is not triggered, even if you give some input data, it will not change the data stored inside the flip-flop nor will it change the output Q or Q'. Now there are basically two types of triggering. The triggering is given in form of a clock pulse or gating signal. Depending upon the type of triggering mechanism used, the circuit will become active at specific states of the clock pulse.
Level Triggering: In level triggering the circuit will become active when the gating or clock pulse is on a particular level. This level is decided by the designer. We can have a negative level triggering in which the circuit is active when the clock signal is low or a positive level triggering in which the circuit is active when the clock signal is high.
Edge Triggering: In edge triggering the circuit becomes active at negative or positive edge of the clock signal. For example if the circuit is positive edge triggered, it will take input at exactly the time in which the clock signal goes from low to high. Similarly input is taken at exactly the time in which the clock signal goes from high to low in negative edge triggering. But keep in mind after the the input, it can be processed in all the time till the next input is taken.
That is the general description of the triggering mechanisms and those also apply to the 8085 interrupts.
One reason we clock flip flops so that there isn't any chaos when the outputs of flip flops are fed through some logic functions and back to their own inputs.
If a flip-flop's output is used to calculate its input, it behooves us to have orderly behavior: to prevent the flip-flop's state from changing until the output (and hence the input) is stable.
This clocking allows us to build computers, which are state machines: they have a current state, and calculate their next state based on the current state and some inputs.
For example, suppose we want to build a machine which "computes" an incrementing 4 bit count from 0000 to 1111, and then wraps around to 0000 and keeps going. We can do this by using a 4 bit register (which is a bank of four D flip-flops). The output of the register is put through a combinatorial logic function which adds 1 (a four bit adder) to produce the incremented value. This value is then simply fed back to the register. Now, whenever the clock edge arrives, the register will accept the new value which is one plus its previous value. We have an orderly, predictable behavior which steps through the binary numbers without any glitch.
Clocking behaviors are useful in other situations too. Sometimes a circuit has many inputs, which do not stabilize at the same time. If the output is instantaneously produced from the inputs, then it will be chaotic until the inputs stabilize. If we do not want the other circuits which depend on the output to see the chaos, we make the circuit clocked. We allow a generous amount of time for the inputs to settle and then we indicate to the circuit to accept the values.
Clocking is also inherently part of the semantics of some kinds of flip flops.
A D flip flop cannot be defined without a clock input. Without a clock input, it will either ignore its D input (useless!), or simply copy the input at all times (not a flip-flop!) An RS flip-flop doesn't have a clock, but it uses two inputs to control the state which allows the inputs to be "self clocking": i.e. to be the inputs, as well as the triggers for the state change. All flip flops need some combination of inputs which programs their state, and some combination of inputs lets them maintain their state. If all combinations of inputs trigger programming, or if all combinations of inputs are ignored (state is maintained), that is not useful. Now what is a clock? A clock is a special, dedicated input which distinguishes whether the other inputs are ignored, or whether they program the device. It is useful to have this as a separate input, rather than for it to be encoded among multiple inputs.
Best Answer
Something that triggers on an edge only triggers for an instant. Something that triggers on a logic level will trigger continuously as long as that logic level is there, limited by the propagation delay of the circuitry.
Suppose you wanted a counter to count up once per clock cycle. If it triggered on a logic HI, that's no good because it might trigger thousands of times while the clock signal is HI before it LO again. What you really want is for it to trigger just once when it goes HI and then stop, and not trigger until it goes LO then HI again, but that's what an edge is.
You basically can't level trigger off of anything that is a clock because nothing will stay synchronized. You need to edge trigger.