What does the conjunctive AND/OR really mean in any given sentence?

Question

For example, please submit your high school transcript AND/OR college transcript.

Answer 1

To explain I will use your sample sentence.
The person asked you for a transcript.

and=both transcripts
You can submit your high school transcript AND your college transcript.

or=only 1 transcript
You can submit your high school transcript, OR you can submit your college transcript.

Answer 2

It means you can do any of these (your decision):

a. submit your high school transcript and your college transcript

b. submit your college transcript

The instructions were written by someone to cover all possibilities.

You could be applying with only a high school background.

Or you could be in college somewhere and want to transfer to this new college - in which case they would want to see your transcript from your current college.