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Emergent (evolved) systems use (to their benefit!) a great deal of interacting parts, with complex interactions, and with complex parts. Economies, ecologies, the Internet; to some degree, neural net AIs.
It’s possible to set aside the question of evolution vs creation, and just notice that these two categories exist, and we’re clearly in the latter.
Evolutionary biologists have very detailed answers to all of these questions, plus a bunch more that are far more complicated and confounding to laypeople. You can even find some great popular science books that hold your hand and walk you through some of the absolutely mind-boggling ways in which we have found evolution to work. It doesn't require any advanced math courses to wrap your head around if you go at the topic patiently and with an open mind.
The numbers and timescales on which evolution has been operating are astronomical, far too large for a human mind to comprehend in any meaningful sense. Of course it's products are also going to be a challenge to comprehend. Especially if you start forming opinions before you have consulted the experts and put in the hard work of trying to learn how those experts know what they think they know.
It's strange that an uncoordinated, random walk of mutations would keep a profound number of changes in tact, ready for some other random bit to take place and it all just "fall into place". The eye didn't evolve. Hearing didn't evolve. Smell didn't evolve.
These explanations are always full of "must have" and "must have been". This line of thinking is just hopeful projections of desired causality.
Hearing is just vibration- and motion-sensing. It evolved from the lateral line in fish, which is not limited to "hearing" per se, but detects motion—current and transient pressure waves that might indicate predator or prey swimming nearby.
Smell is just chemical sensing. Catfish have chemoreceptors across their bodies.
A lot of intermediate forms are impossible to present to you as evidence because all we have is the fossil record which generally doesn't include soft tissue, which is where most of the interesting stuff happens.
One mutation that enables the slightest bit better sensing, provides an advantage, and offspring of that species in that area will gradually end up with that adaptation. Then it repeats. The "must have" is not dictated by some agent, but by environmental selective pressure, relative to pre-mutation versions of the same organism. It's induction, but for biology rather than math/cs.
It's quite possible that other types of photon and vibration and chemical sensing could have evolved, and would be superior, but we started down a path that locally descended to where we are now. And the existing tree of life would predate or out-compete pretty much any new multi-cellular life that tried to "experiment" and "evolve" novel sensing organs.
You want to talk about just-so stories? Cephalopod eyes attach to the optic nerve on the opposite (back) side of the retina, so they have no blind spot. Did a designer goof up on vertebrate eyes and not fix it, but instead implement a very complicated neurological fix involving saccades and "blinding" our brains to the instantaneous hole in our vision?
An appeal to incredulity is not an argument.
>These explanations are always full of "must have" and "must have been".
Any explanation that starts with "must have" requires that there is a single theoretical framework that could possibly apply to the world as we see it today. Since you reject this necessity, you must think there's an alternative framework that accounts for all observed phenomena (or that accounts at least as well as the theory of evolution). What is that framework?
It IS strange, using the evolutionary framework itself, that useless mutations will hang around for thousands or millions of years (countless generations) before dropping perfectly into an extremely complex system, that itself is but a small part of a larger complex system.
Evolution teaches that small, immediately useful mutations build upon one another, reinforcing the beneficial nature of the mutation. It's impossible to build large, complex life systems (with a large number of prerequisites at each step) this way. For example, the Heart, Blood Vessels and Blood. They're each extremely complex but useless without the other two.
How would evolution slowly evolve a heart with no blood or blood vessels?
How would evolution slowly evolve blood but no blood vessels or heart?
How would evolution slowly evolve a network of blood vessels but no blood to carry or heart to pump?
Yes. Now. Not when they first emerged.
>but useless without the other two
Unsubstantiated assertion.
>How would evolution slowly build a heart with no blood or blood vessels? How would evolution slowly build blood but no blood vessels or heart? How would evolution slowly build a network of blood vessels but no blood to carry or heart to pump?
You start with a fluid-filled body cavity where oxygen is transported by dissolution from the outside to the inside. This fluid already contains oxygen-transporting cells. Then you section off part of the cavity to enable oxygen-transporting cells to move more efficiently. At this point the OTCs are completely separated, so the fluid inside the conduits can be called blood. The animal can pump blood by squeezing its body during its normal locomotion. Eventually muscle cells are added to the circulatory system to enable oxygen circulation independently of the animal's movement, as well as to circulate it even more effectively. Later on the muscle cells become centralized as it's more efficient, not to mention that a big single muscle can pump more strongly than a distributed system of tiny muscles. Each step of the way you have a functional organism and each form performs the function of transporting oxygen more effectively.
I know you're going to say that this is a "must have" explanation, but you merely asked for an explanation. The above is a plausible series of events that could have led to the circulatory system as we see it today, so if you want to argue that the circulatory system couldn't have evolved, you'll need to argue why this explanation isn't plausible.
EDIT: Also, I can't help but notice you ignored the question I asked in my last paragraph.
Similarly, simpler versions of, e.g, eyes have been observed in nature with structures that are thought to be analogous to those of our early ancestors when eyes were first developing.
If each step from simple to complexity is using this randomness evolution, it will be more and more defies law of probability.
Wikipedia said earth had water 4.4B year ago. The first cell formed 3.8B years ago. This PBS video[2] said multicellular life emerged 1B years ago. Other source said 1.7B years ago. And then the first modern human appeared around 300 thousands years ago. So the question is: is 700M-1400M years enough time for the probability to create human?
When you have a selection mechanism, the randomness of mutations becomes kind of moot. Each step of the way that produces a new adaptation only has a handful of optimal (or optimal-enough) solutions. Now, suppose that we're an underwater species that's in the process of developing light-sensitive cells, and from our present genome there are 2^64 possible genes that will produce a good protein for the transduction step (of converting light into some other form of energy). Do we need to mutate 2^64 times to find the "correct" gene? No, all of those 2^64 genes are "correct". Our descendants should not fall into the trap of thinking that because they got gene #5541741487894936799 that it was a special outcome. They could have just as easily gotten gene #5541741556614413535.
Evolution is not random. The mutations that make it possible are, but natural selection makes it a non-random process.
If you make a random number generator, but keep more of the odd numbers, you'll get a non-random result set.