Simple question but very intriguing one. Thanks for asking. Let me try to answer with an example so that it helps to understand better.
“More” is used when there’s a definite measurable items in sentence. Let’s say “add two more apples” “ten more miles to go” etc.
“Most” is used when there’s an indefinite items in sentence. Let’s say “most of them made it on time” etc
Hope this helps. Thanks.