I Have A Question About Copying Record Please

I have two tables, one is called Table A and the other is called Table B:

Table A contains these data:
I
II
III

Table B contains no data

in the form of Microsoft Access, I want to be able with a push of a button and DEPENDING on the selected item, I want that selected item to be copied into table B. For example, in table A I am selecting item II, when I push the button copy, I want that item to be copied into table B.

So the result will be:

Table A Table B
I II
II
III

How does one solve this problem please?