homework - ph & pOH - Autoionization of Water

So I was learning about pH and pOH and it made sense. I looked at strong, weak acids & bases and learned that they dissociate completely in water. So then I moved on to water and learned about the autoionization of $\ce{H2O}$.

Here is the process:

$$\ce{H2O + H2O -> H3O+ +OH-}$$

So then I learned about the equilibrium constant and then I figured this: $$\ce{{[H3O+][OH-]} = 1E -14}$$

What does this mean?

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So after that I was doing some basic pH and pOH calculations withe strong acids and bases.

Here is one of them:

Find the pOH of a $\ce{1E-6M} \ce{HCL}$ So here are the steps:

$$\ce{-log[1E-6M] = 6}$$ Ok so the solution had the pH of 6

At first I was like that's nice and I proceeded.

$$\ce{6+pOH=14}$$ $$\ce{pOH=8}$$

So then I was like wait a minute where did the $\ce{OH-}$ come from if it dissociates like this:

$$\ce{HCl + H2O -> H3O+ + Cl-}$$

So then I thought about it and this is what I came up with:

Since there is some $\ce{OH-}$ then there must be some water more water that autoionized into OH and that is the only place where $\ce{OH-}$ could've come from. So that means that even though $\ce{HCl}$ completely dissociated there must be more water than $\ce{HCl}$, because referring to the original equation there is $\ce{1M}$ quantities of $\ce{H2O}$ and $\ce{HCl}$ and so in the $molarity$ of the $\ce{HCl}$ given that means there was more water and less $\ce{HCl}$ and the $\ce{OH-}$ could've only come from the autoionization of that excess water.

So that is what I thought could be the only possible explanation of the $\ce{OH-}$ in a strong acid. And that could only come from $\ce{H2O}$ .

So am I right, and If I am wrong then please tell me where the $\ce{OH-}$ came from.

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Why is the $\ce{pH}$ scale only to $14$? Because if I took a $\ce{2M}$ $\ce{HCl}$ and then I get a super acid in which the $\ce{H+}$ ions is a lot more than the $\ce{H2O}$ available to absorb them. So why is it only to $14$? Does it have to relate to the original autoionization of $\ce{H2O}$?

And If I totally grasped this wrong then can you please accurately tell me what $\ce{pH}$ & $\ce{pOH}$ and what autoionization of $\ce{H2O}$ is for a beginner and still make sense.