Doubt: Contract vs Quasi-contract - Kitna confusion hai

Yar samajh nahi aaya, please help! Maine Contracts ke Class mein baithkar ek sawal ka jawab nahi paya. Quasi-contracts aur Contracts dono hi contract ke under aa sakte hain, lekin yeh to dusri cheez hai jo kuch log keh saktay hain. Quasi-contract woh hai jab parties ke beech ek agreement hota hai, lekin kisi niyam (law) ke under, jaise ki Section 68, 69, 71 ke under. Iske beech hi, agar dono parties ke beech direct agreement hota hai to yeh ek normal contract ho jaata hai. Lekin agar parties ne koi agreement nahi sign kiya, to kya yeh quasi-contract ka case hai?