Logic operators -- or

I need some help.
I need to understand how the OR FUNCTION works!

I have a foreign key and then I want to relate this foreign key with a letter.

if ‘thisforeign key’==‘1’ then ‘A’ or ‘B’ end

it doesn’t work!! I don’t know if this is possible but if you can help!

Thank you

Do you mean “if the value is 1 then use A, otherwise use B”? In that case you want:

if this_foreign_key == '1' then 'A' else 'B' end

Thank you for your answer .
I mean
if this_foreign_key == ‘1’ then ‘A’
and if this_foreign_key == ‘1’ then ‘B’
elsif this_foreign_key == ‘2’ then ‘C’