How do you purchase a property "Subject To"

I keep reading forums/articles here on bigger pockets explaining how to purchase a property with no money down but I really can't find an in depth step by step explanation. Many times it's subject to so I would like to know how do you even find a subject to deal? I spoke to a few RE agents and asked if they had sellers willing to go with "subject to" but all brushed it off as if it doesn't exist. What do you say? Who do you say it to you? And how do you say it? I want to start investing already but the more I read the more confused I become. RE professionals are showing me that I'm going about things the wrong way yet won't show me the right way. Another question would be how can i find a mentor with "no money down" -_-