It's always great to kind of look into information on Youtube like Rolando mentioned and Jerry is a great source to start. Clear and to the point, I will answer your question and have it listed below. But be sure to look into questions yourself because nine times out of ten there are other individuals that ask the same question. You just sometimes have to be resourceful on finding answers.
When you find an off/on market property, you want to work with directly to the seller and send them an offer. Your contract will vary state to state. I'm in Texas and we traditionally use TREC.
Offers can be written up with this simple formula but this is not what I use just understand quite a bit of people use this offer calculator. ARV *.70 - Repairs - Assignment Fee = Max Offer. If the Seller Accepts you then enter an agreement with them.
You then have the right to sell that agreement to an end buyer and make an assignment fee. That's the most vague definition of what you asked.
When you have a moment do some more research or read "If you can't Wholesale after this I have nothing for you".