I have seen people pouring rose water and all kind of things into the grave before or after laying the dead body. Please advise exactly what is to be done along with the related Hadiths.

The concept of pouring rose-water over the grave is baseless. Nowadays, this has become a custom and is considered necessary. Thus it is a Bid'ah (innovation) and must be avoided. Rasulullah (Salla Allahu Alayhi wa sallam) said, Whoever innovates something in Deen is rejected. (Mishkaat)

and Allah Ta'ala Knows Best

Mufti Ebrahim Desai