Ever viewed movie mistakes for a chuckle? When we were kids, we'd watch for the actor who forgot to take off their wrist watch in a period movie.
Basically, that is what a content editor does. They look for flaws in the timeline, people who teleport to another location, and it isn't SciFi or Fantasy. They look for name, eye color, and hair color changes. And, a million more things like would that word [a recently born word] be used at that time, or by that person. There is fact checking and the critical eye for oops moments that an astute reader would catch.
My husband was discussing the "it" book of the week with his great aunt. She had read it, or had started to read it. When the main character went for a walk at 2 AM and the moon was rising, she threw the book in the lit fireplace. The topic of conversation rapidly changed course. Later one of our boys asked why she had thrown the book in the fire. Little boys don't know that the moon doesn't rise at 2 AM, neither did that writer, or their editor.
Inexperienced writers who upload their book on one of many free publishing sites rarely seem to have had their manuscript in the hands of a content editor. Some seem to think their high school English teacher looking it over is sufficient. Well, it isn't.
I rely heavily on the Certified Proof Reader [line editor] at Cactus Rain. She knows grammar rules that I've never heard of, and probably wouldn't understand. But she is the first to tell her private clients that she does not do content editing.
What a writer should do, and usually won't, is print two copies of their manuscript, find a willing helper, and read the whole thing aloud. The helper should follow along and catch things that were read differently from the print. Also, if they are honest, they will say when something doesn't make sense, is repeated too often, or is simply flat out wrong.
So that's the tip for the day. Read your ms out loud from a printed copy. You'll be amazed. And, your manuscript will be greatly improved. Happy writing and editing.