Mandala offering is a special vajrayana method to accumulating merit. Here, the mandala is a representation of the universe – visualized as a pure realm, filled with all desirable and precious objects – which we offer to the buddhas and bodhisattvas, to the objects of refuge.
For daily mandala offering or the accumulations of the preliminary practice, one uses a mandala base plate and offers heaps of grain and precious stones while chanting the offering prayer.