Let me try. "In," "into," "onto," and "on" are location words. "In to" and "on to" are not usually both location words (only the first is).
"Into" usually means "within." I climbed into the bed. (I got under the covers). "Onto" usually means "on top of') I climbed onto the bed. (I stood on top of the bed).
Regarding into, in, onto and on I still have a few questions...
If someone says for example Ben will look into this problem. Is that correct? or. I will have a quick bite and I will get onto it or should it be into it?
Here we are seeing the metaphoric use of the words "into" and "onto." So the speaker is not actually getting into or onto. He is doing so in a figurative way. This use is more idiomatic.
I will look into this problem. (The problem is like a car and I will open the hood and look into it).
I will have a quick bite and then get onto it. (The job is like a horse an