First, to answer your questions:
1. Getting a property under contract is exactly what it sounds like. You and your seller sign a contract detailing the purchase price and terms you agree on. In general there is no money involved in this part it's literally just signatures (except earnest money, but most wholesalers either don't put any earnest money down or put a relatively small amount like $20-$500). There are purchase contracts in the file place. Go read through them to get an idea what you'll be dealing with. I recommend seeking legal counsel when it comes to actually drafting a contract to use.
2. Yes you can get an REO under contract. But banks will not allow contract assignment so your best bet is back to back closing. In other words, you buy it, then resell it.
Some personal notes:
Go ahead and get that notion of wholesaling with no money out of your head. It's a lie. You have to put something in to get something out. True, you can technically wholesale with little money, there's certainly less money needed than to actually invest. But nothing in this world is free. At the very least you'll need money for marketing. Lots of people spend thousands of dollars just sending out their first mailer.
On that note, it is very possible to spend very little and be successful ("very little" being a relative term; obviously $500 is pennies compared to buying a $6MM multifamily, but if you are unemployed and struggling it can seem like an impossible amount). HOWEVER like I said you have to put something in to get something out. You will have to put in a lot of time and effort in order to save money.
When you say you "can't actually afford to purchase anything"...are you sure? There are plenty of ways to buy without having $200k cash in hand. What happens when you get a contract and don't have/can't find a buyer?