How do I buy Duplex, Triplex, Quadplex?

[Sung Won Moon]

Hello everyone, 

I first want to apologize if this is the stupidest question you've seen in the forum.

I'm a complete newbie wanting to househack with small multifamily. And my first step was to find them on Zillow to get an idea. If I'm understanding correctly, every duplex sale that is listed in Zillow has only one apartment of duplex listed. So does that mean 2 apartments of the duplex needs to be listed in order for me to own the duplex?

How should I start finding the deals? 

Thank you so much in advance!