Questions about Wholesaling

[Ethan Bowdoin]

Can somebody explain to me how exactly wholesaling works? I understand you are assigning a contract to your buyer, but when you offer to purchase the property for say 50K then you sell it for 70k at what point is the original seller paid? Do you pay them the 50k up front? Or do you pay them the 50k after you sell it for 70k then just keep the extra 20k? I am just confused on the process and how to do it.