What use are our wisdom teeth to us? And why haven't we evolved to not need them?

The most common theory is that human ancestors ate more plants and needed the extra molars to help grind down the plant material. As human diets changed, we didn't develop as largeand now they aren't quite big enough for wisdom teeth. This makes them a vestigial body part - a part that is no longer really useful for an organism, but has stuck around. We haven't evolved to not have wisdom teeth because the evolution of our jaw happened faster and having the extra wisdom teeth wasn't enough of a disadvantage to our ancestors that those without them were able to pass on their genes significantly more successfully.

Generally, I think the better question for evolution is "why did this evolve?" rather than "why not this?" A lot of times we can't know why something did not evolve because evolution often comes from random mutations so whatever evolutionary trait that happened to pop up is the one we get. However, we can usually make a good guess as to why a particular part of the body was useful.

Why can't we choose to rotate our eyes individually like a chameleon?

The same reason we don't manually control our digestion system: We have no need to.

Deeper explanation: Predators have their eyes both facing forward so they can judge distance (depth perception) when hunting prey. If we want to look left, we can look left. If we want to look right, we can do that too. It doesn't take long for you to look left and right and have an idea of your surroundings. Whilst true that it takes more energy to keep looking left and right, the quality of our vision is better because you have this contant depth perception.

Animals which are hunted from all directions (like fish) have eyes on the sides of their head so they can have a greater arc of vision to see oncoming predators. This requires less energy, but they have no depth perception. Luckily, they don't need it. They don't need to know how close a predator is, they need to know WHERE it is, and swim as fast as possible in the opposite direction.

We're predators. We need to see what's infront of us so we can hunt and navigate more easily.

How do microwave ovens generate microwaves?

Why is it that a person can't take a large amount of over the counter pain relievers, like Tylenol or Ibuprofen, to get the same effects as stronger painkillers like Vicodin or Hydrocodone?

Different method of action. Opioids like hydrocodone and Oxy work by binding to neuroreceptors(neuro means brain) which send a depressive signal, which basically means that the signal numbs your central nervous system.
I don't remember the exact MoA of the others so to just put it simply, ibuprofen and aspirin work by reducing inflammation in your body, and Tylenol works by simply cutting off the pain signal on its way to your brain.

How apes with a similar muscle mass are so much stronger than human?

There's a few reasons but functionally most of them come down to finer muscle control. If you look, for example, at muscle bundle innervation we control much finer sets of muscles at a time. Great apes, on the other hand, fire larger bundles at once resulting in stringer but jerker motions. Mechanically speaking there are ask changes in insertion points to control leverage advantages vs mobility advantages as needed. Just watch a chimp doing things that require fine control and they look very clumsy compared to a human. Also, keep in mind that there's learned flexibility in both systems and humans can be quite strong and some chimps have learned to be quite dextrous (I.e. The differences of the distributions are further exaggerated by the tendencies of the species). Basically though, you're seeing the result of 6 million years of evolution in support of shorter reproductive cycles & increased intelligence and took use, the musculature and nervous system changes were critical to support those advancements.