Give authorization to some one else

I am now making an application connected to the firebase. Every person has his own account and has a list of data. He adds it, so I want someone to send invitation to you, please, so that he has access to see this list and amend it, and you hear at the two, whoever was the person who amended it. I mean, someone X, I sold to Y, he says, "You have access to my list, so someone Y sends him a notification, so if before he leaves Y, he has the possibility that he sees list X and edits in it, and when he edits X, he sees the edit." This is how I sent an invitation to be able to take the Access??