@Orochi5
Friday is a cannibal, from one of two warring tribes that live on nearby islands. IIRC, he has been captured by the other tribe, and Crusoe kills the captors to save him. To show his gratitude, Friday carves out the heart of one of the men, and offers it to Crusoe, who is horrified and refuses it, so Friday eats it himself.
It was many years since I read the book, so it might not be 100% accurate, but it's the gist of their meeting and the circumstances. "Friday" is what Crusoe calls the man, for reasons I don't remember.