We experience the world and that is more than just processes in the brain, it is contents of consciousness.

There is a direct correlation between brain processes and our first hand experience of the world. If your brain no process, you no experience. If your brain processes differently than it did a minute ago (say, with the help of some psychoactive substances or a really solid kick to the head), then your experience also changes.

Hell, you can verify this yourself without any drugs, swift kick, or special equipment. Just hold your breath until your brain is starved of oxygen enough that it can't process normally and stars will begin to appear.

There's no doubt that neural activity IS what we experience, that brain processes and our experience ARE one in the same.

However, the subjective experience content of a mental state can neither be captured through measurements nor expressed through words.

Scientists are now imaging what someone is experiencing from brain waves. I totally sh*t you not. So... yeah, it can be captured and shown using EEG.

*"When we see something, our brain creates a mental percept, which is essentially a mental impression of that thing. We were able to capture this percept using EEG to get a direct illustration of what's happening in the brain during this process," says Nemrodov. *

https://www.sciencedaily.com/releases/2018/02/180222145037.htm

Everything feels different for everyone in a certain way when we experience something.

Colors feel like I'm really, really, really HIGH.

... we could never be sure that your red is also my red.

I understand now! That whole bit that doctors do to diagnose colorblindness is just new age hoooey! How could I have not seen it before! (massive sarcasm)

Colors are created in the brain by different wavelengths of light.

Yes, that's right, light shines directly into our brain. I need to rip out that whole bit about sense perception from my psychology 101 book. It's garbage, apparently.

But how should i know that your experience of red is the same as my experience of red? The answer is: not at all. That is impossible to know

Repeating this doesn't it make it any more true or profound. I've already pointed out two ways.

The psyche of others is unattainable for us.

Not entirely, as I've pointed out. Here's another reference: https://en.wikipedia.org/wiki/Thought_identification

Or maybe you're trying to point out that the human species aren't capable of telepathic mind reading. Oh, wait.... scientists are even doing that now.

https://www.sciencealert.com/brain-to-brain-mind-connection-lets-three-people-share-thoughts

The chaos of black spots suddenly becomes a meaningful structure. Only by the memory of the other picture.

You could perhaps have asked "do you see a mustachoid man in this seemingly random bit of dots?" At any rate, this is a classic example of perception, not consciousness. It's the sort of thing you see in psychology 101.

And surely you also know the pictures in which two or more different things can be recognized. These pictures show you how subjective the things are.

This isn't at all what those pictures demonstrate. They demonstrate two competing interpretations of the same image. Again, this is from the perception chapter of any psychology 101 book. If you mean, "this shows that your perceptions are the result of a perceptual process and thus bullshit to begin with", then I agree with you. Alas your first sentence :

We experience the world and that is more than just processes in the brain, it is contents of consciousness.

But I digress...

Our brain creates our reality and only to this reality we have access.

A++

We experience things outside of us, although they arise in us in our brains,

Dammit! You had it right! Now you introduce a hell of a contradiction.

I'll go ahead and give the spoiler. We don't experience anything "outside of us." It all happens in the brain. We experience something waaay down the pipeline from sensory nerves, but what comes through those pipelines are unprocessed (or at least, in the case of the optical nerve, underprocessed) neural impulses.

It is not easy to become aware of this.

It's not easy to become aware that you're reading neural impulses now, and not words.

The question that arises naturally is, how does this experience arise?

That would be the hard problem. Well, not really, you forgot something. I'll add it...

The question that arises naturally is, how does this experience arise from neural activity?

I will now answer your concluding questions:

Is it due to the complex arrangement of matter, i.e. a materialistic explanation?

Yes.

Or is consciousness perhaps the basis for everything at all?

Yes.

The two are not mutually exclusive.