The most commonly practiced religion by Cambodians is Theravada Buddhism. Some 95% of Cambodians are Buddhists, with the rest being Christians and Cham Muslims. Confucianism and Taoism are also practiced by the Chinese community.
Theravada Buddhism is the oldest surviving Buddhist school, and its teachings are also practiced in Sri Lanka, Thailand, Myanmar, Laos, Malaysia, Vietnam, Nepal, Indonesia, Philippines, and certain parts of China. Theravada is descended from the Tamraparniya, which means ‘the Sri Lankan lineage’.
Buddhists believe in a constant cycle of death and reincarnation, and the ultimate goal is release from suffering, or a state of Nirvana. Nirvana is the end of the cycle of death and rebirth, a state of enlightenment only achieved by earning good karma through virtuous deeds.
Many Cambodians volunteer for services at temples and offer donations as part of religious reverence. It is not uncommon to find boys becoming monks or temple servants for a period of time to better follow the Buddhist path.
Sources: Wikipedia and Tourism Cambodia