Down payment question

[Casey Randall Lenz]

I'm new at this, still learning how to properly get into renting.

I read about people (even young people with no money, supposedly) buying something like a duplex, or condo, or something similar and renting it out. And then 2 months later, buying another, and then in a year they have 7 rental properties or something. Financing is not an issue, I have 800 credit score, decent income, and some good friends at the bank, but what are these people doing for down payments?  I could write a check for 15K and buy my first one, but then I would have to save up for another year to have the down payment for the next one.  To have 7 houses in a year you would almost have to drop 100K out of pocket just in down payments.  So either you have a bunch of cash to begin with, or there is a way around the down payment issue.  Can somebody explain or direct me to something that explains how this works or what these people are doing?