How exactly does networking work?

Hi all,

I am an international student currently studying in the US and aspiring to work in trading after college graduation.

I have been told that networking is the most important aspect of job search, particularly in finance. I know the logistics of networking i.e. I open my college's alumni directory or go on LinkedIn and ask the alums if they want to talk to me about their career paths etc. Ideally, the conversation(s) should establish rapport between us and somehow induce the other person to refer me for a job, but I should never ask for a job referral directly.

What I don't understand is how can one or two phone conversations make someone like me / get to know me sufficiently that they refer me for a job?

I have done several of these conversations and they never led to anything. I obviously cannot become friends with the alumnae because we have never met, age difference, different interests, etc.. To me, it seems that networking is only useful if you were somehow friends with the other person beforehand, so that they are familiar with your personality and knowledge.