It refers to what both (you & I) have in common, indicating that there is no difference when it all comes down to what actually matters. 서울이나 부산이나 생활비는 비슷하다: When it comes to cost of living, there is hardly any difference between Seoul and Busan.

It means Also you and I (but that form is more like also you ,also i but you don't use that form in English)