Traditionally and ultimately the Vietnamese practice ancestor worshipping. This still plays the most important part of the Vietnamese spiritual life. This tradition actually helps make the spiritual life and religious life in Vietnam very characteristic and colorful. Besides the Vietnamese also practice the worshiping of the Mother of the Land.

But Thap Buddist Pagoda in Bac Ninh Vietnam

The predominant religion practiced by the Vietnamese is Mahayana Buddhism, which is often referred to as a way of life or a system of ethic values rather than a religion.  It advocates moderation in all facets of life and sees material objects as standing in the way of greater happiness. Buddhists believe in reincarnation, with the actions of your current life determining the role of your next life. By living simply and selflessly, a person will be reincarnated many times over. This continues over many lifetimes until the soul reaches a stage of eternal happiness - nirvana. 

Temple of Literature in Hanoi Vietnam is dedicated to Confucianism, more of ideology than a religion

Other religions practiced in VietNam are Confucianism, Taoism, Christianity (both Catholic and Protestant), animism, Caodaism, Hoa Hao. A small number of the population practices Islam. 

Notre Dame Cathedral for Catholicism in Saigon Vietnam

One thing the traveler may  find out when traveling in Vietnam is that people follow polytheism even though the majority would tend to say they are Buddhist.

Religious practices for Foreigners
Ha Noi's large Catholic Cathedral has services only in Vietnamese; another Catholic church, the Cua Bach Church, near West Lake has a Sunday morning mass in English.