How do you when to end each chapter? How do you space each one out? Thank you!?

You are the story teller. We just have to wait and see what you do.

I remember a story where one chapter ended in the middle of a sentence, and the next chapter finished it.

I remember a story that began with chapter three.

You need to read novels. Lots of novels. Any novels. Notice that they all have perfect spelling, perfect punctuation, perfect composition. Notice where they use one space and where they use two*. Notice that every speaker in a dialog gets a new paragraph, and every paragraph is preceded by a blank line. Notice any writing techniques or figures of speech. Take notes so you know where you found what you know. It takes a lot of reading to be a writer.

*It's actually a space and a half, so don't get hung up on that detail.