Why does heat transfer from hot body to cold body? Can it transfer in the opposite manner?

yes if u want to see it molecularly, if u heat a body, its molecules start vibrating. So if u compare two simillar bodies at temperatures T1 and T2 where T1>T2 then, in first body, molecules vibrate more aggresively than second. clearly, they cannot gain more energy to less aggresively vibrating molecules. They can only give energy.