I'd like the detailed explanation of quid pro quo?

Quid pro quo is a latin phrase that means "Something (Quid) for (pro) another (quo)" so it means You give me something, I give you something, or an exchange of two things. It is used in legalese as way to explain collaboration and conspiracy. One person get something in exchange for another thing. E.g. I give you testimony and in return you give me a reduced setence. So it just means one thing is exchanged for another thing. "You do me a favor, I'll do you a favor." That is quid pro quo.