Short answers, pulled from the story.
The Three Jewels, also called the Triple Gem, Three Treasures, or Three Refuges (Pali: ti-ratana; Sanskrit: tri-ratna), are the Buddha, the Dharma (Buddhist teachings), and the Sangha (the community of followers). Taking refuge in all three is the foundational act of Buddhist practice shared by all major schools.
Taking refuge is a recitation or prayer performed at the start of a day or a practice session. In early Buddhist scriptures it expresses determination to follow the Buddha's path but is not a surrender of personal responsibility. Lay followers often take the five precepts in the same ceremony.
The five precepts are: not killing, not stealing, not misusing sex, not engaging in false speech, and not indulging in intoxicants. A layperson who upholds all five is described in the Pali texts as a 'jewel among laymen.'
Mahayana expands all three categories. The Buddha jewel includes innumerable Buddhas such as Amitabha, Vajradhara, and Vairocana. The Dharma jewel includes Mahayana sutras and tantras in addition to the earlier Tripitaka. The Sangha jewel extends to advanced bodhisattvas like Avalokiteshvara, Vajrapani, and Manjushri.
The Ratnagotravibhaga argues that the Dharma as doctrine is ultimately abandoned like a boat, and the Dharma as cessation is merely an absence that cannot function as a refuge. The Sangha still relies on the Buddha for its own refuge, so it cannot independently serve as a refuge for others. Only the Buddha jewel, which possesses the Dharmakaya and neither arises nor disappears, is considered an eternal and lasting refuge.
The Triratna is a Buddhist symbol representing the Three Jewels. It is composed of a lotus flower within a circle, a vajra, an ananda-chakra, and a trident with three branches. At Sanchi it appears in frieze sculptures dated to the 2nd century BCE, making it at least 2,200 years old in its documented form. It also appears on coins of the Kuninda Kingdom from the 1st century BCE.