I asked a Ngakpa once (a bon/buddhist practicioner who is practicing Vajrayana) and he said that communication with spirits works via visualisation and energy.
For example, a smoke or incencse offering is visualised as cleansing and purifying the environment, the smoke may transform into good and useful things for the non-physical spirit world in your visualisation and also the practicioners energy and intention is important. The energy of giving to those in need without expecting any return is very important in bon and buddhism. This type of generosity is very pure, positive energy.
The positive emotional energy out of which an offering is made for the well-being and benefit of the spirit world is said to be helpful for these being.
Great questions. In Bon, the sang (smoke) offering is usually done in the morning and together with different visualisation the smoke is actually transformed in the visualisation into offerings for all classes of nature spirits.
At midday, the Chutor (water offering) is made mainly for the Naga spirits (water spirits).
In early evening, the sur-chod (fire offering) is done by offering Tsampa (barley flour mixed with other vegetable offerings) into the fire and thus producing pleasant smoke scents. Mainly for the dead. Spirits in transition and - I think - also so-called “smell eaters”, spirits who appreciate pleasant smells.
The Chöd offering (body offering) is usually done in the later evening and the practicioner visualises the offering of his/her own body to the spirits of a wild place.
In Yungdrung Bon and buddhism, there are no animal or blood sacrifices, they are rejected, and it is believed that they are not necessary either. Even wrathful, “rough” spirits can be pacified by these energetic transactions.