Subject to? any knowledge would be greatly appreciated

[Elvis Genao]

Hey BP community hope all is well! in my investing journey i have stumbled upon the term " subject to". Im from the Westchester NY area. I own a co op and planning to rent due to a growing family. I also have a new job which its making it hard to get a loan. No dept great credit. My question is how do i even go about this? Do i contact local realtors? Do i look for foreclosures? also i feel like it would be near to impossible to get this done because the seller could just choose people they know? any thoughts? 

Thanks guys !