Animism

Animism is the idea that all objects (including sentient beings) have a soul (linh hồn) or some sort of spirit. This developed in Vietnam before Buddhism, Confucianism and Daoism. Vietnamese animism in particular believes in spirits in nature (Thần linh). Thần (deities/spirits) are worshipped to be the protectors of villages, forests and water sources. Ancient banyan trees (cây đa) aswell as large rocks are believed to be the residential sites of spirits, particularly for their 'eternal', long-living nature and people often make offerings to them.

Spirits

Next, you have the ancestral spirits (Gia Tiên) and human, deified heroes acting as middlemen between the divine and the living. They are worshipped for their protection, guidance and ability to alter the luck of their descendants and communities alike. The dead contine to live on in the spiritual realm, and filial piety (hiếu đạo) is key. Worship keeps ancestors happy, and prevents them from beecoming restless/hungry ghosts (ma) who bring bad luck.

There are three types of ancestors, Gia Tiên, basically deceased parents, grandparents, etc. Tổ Tiên (clan ancestors) are the founders of family lineagues and oftentimes worshipped by dedicated clan temples (nhà thờ họ) by rich noble families. Lastly, there are the Hương Linh (anonymous ancestors) who are forgotten or unclaimed souls who are sometimes given offerings during the Vu Lan (Ghost Month) festival so they don't suffer in the afterlife.

Household Spirits

Prominent household spirits include Thổ Công (the Land God) who protects the household and honored via a small altar in one's house. Táo Quân (Kitchen Gods) are three spirits who watch over the family and report to the Jade Emperor about what's happening at Lunar New Year. Ma are also household spirits, and they can for example be wandering souls who died violently/in vain without proper burial etiquette.

Rituals

Common offerings (cúng) include food, votive paper (which is special paper often replicas of wordly possessions burned in the hopes that they'll be brought over to the spiritual realm) and incense given to spirits for blessings and avoiding curses.

Shamanism (Đồng bóng) where mediums communicate with spirits to heal or divine the future and festivals where for example one visits temples to pluck a small branch (lộc) from sacred trees and placing it on an altar to attract prosperity are also animistic rituals.