Hello guys .... Please I heard it possible to buy an appointment date at the US embassy... Please how true is this and how can one go about it ?

I'm a 41 years old man seeking to visit a friend of mine in the USA... She's willing to send an invitation letter and also any other necessary documents to back it up... Please I need your advise on how to go about the whole process, like what and what does she need to send to me and what documents do I need to take with me when going for interview.