Referrals at Banks

How exactly do referrals work? I understand that networking is a big part of landing an internship/full-time role at banks and that referrals can be a way to make sure that your resume is seen, but who exactly is able to give a referral? For example, are analysts able to refer people? Just VPs and MDs? Can an intern that I know really well refer me? Does a referral only help if it's from someone in the same division that you're applying to? If I know I already have a referral at a specific bank, do more referrals look better, or once you get one does it not matter at that point anymore?

The reason I'm asking is because I want to prioritize who I try to connect with at a lot of these banks.